Do you mean algorithmic or just the ability to post orders?
Not sure what you mean by online. If you mean web based or mobile? Or is desktop fine?
Robin Hood isn't bad if you just want point and click.
If you want to do something algorithmic then use Interactive brokers.
You might find something better but IB has been around for ever and probably wont' get out of this business any time soon. I can't say the same for any other broker that a retail investor can use.
Having said all of that, I would really, strongly, emphatically advise against trying your hand at algorithmic trading.
For the average person the rule they should internalize is Investing good, algo trading bad.... and this is comming from one of the people who benefits when the average person tries to trade in the stock market.
http://www.barrons.com/articles/SB51367578116875004693704580...
This is the methodology used for the ranking:
http://www.barrons.com/articles/SB51367578116875004693704580...
This is a comparative table where each broker's offerings are broken down and analyzed:
http://www.barrons.com/articles/SB51367578116875004693704580...
Keep in kind that their product isn't designed for "novice" retail investors. There is a $10k minimum and the trade stations have a learning curve.
Really though, why do you care about real-time trading anyways? Not being sarcastic; this is an actual question.
Let me clarify my position:
I think most people should invest.
And part of that investment should be in the stock market (how big a part depends on their individual age and risk tolerance).
And for most people, the only stocks they should ever buy are ETFs that are passively managed with low fees.
Yes they need to do enough research in as far as to find out that they should only be buying ETFs (and that kind of research does not require any kind of support from their brokerage). But they shouldn't be tempted to do more specific "research" to pick their own stocks because most people who do that are doomed to underperform the market anyways.
So in the end, the fact that Robinhood lacks a decent research platform shouldn't matter to most regular investors because they should only ever buy specific ETFs anyways.
When I first joined the Android beta Robinhood had a very clear message before every purchase: "to protect the user from volatility, Robinhood creates market orders as limit orders with a 5% higher price". So, yeah, that means that if you place your market order at $100, they reserve the right to broker it all the way to $105, which is bullshit. On average it won't be that high, but still, if you were planning to make a 0.5% profit, you'll always lose.
The only way to get around that is by creating a proper limit order yourself, setting the price a couple cents the current price (to match the BP you are willing to give up.)
Since I started doing that, things became way more predictable.
At 2:00EST [daily|weekly|monthly], buy N shares of SPY.
Once you are comfortable with that, just rebalance this portfolio to the 60%/40% ratio once every year or two (http://seekingalpha.com/article/2130243-portfolio-rebalancin...), and start moving toward fixed-income funds as you get closer to retirement.
But you don't even need an account to use it. Just create a paper-trading account and you have access to the application, plus you can play around with trading without actually spending any real money.
Furthermore, dough.com is (kind of) a branch off of ToS - less functionality, but a much prettier interface. You can sign up on dough and get full access (without being able to actually trade, of course) without a brokerage account or paper account at all.
You can trade all types of securities as well. And it's very easy. The mobile app is also top notch.
The only ones who make money in the market are arbitration traders (HFT types) or those who just happen to be on the right side of market. As an individual investor, you will spend lot of time and money to get your systems running - but market conditions will change dramatically and all your backtest algorithms will become irrelevant.
Optionshouse.com is great, for both stocks and options, commissions-wise. Not as good for lightweight, realtime charts. I use OptionsXpress for that purpose.
Optionsxpress has high commissions, so I only use the charts, which are superior. Put in $100 bucks and it'll give you full access to the trading tools.
Algorithmic Trading
I use T4 for day-trading futures. I think it has APIs for C#. But no stock/options, only Futures.
Edit: T4 API link http://www.ctsfutures.com/wiki/T4%20API%2040.MainPage.ashx
1) Flash platform that randomly crashes after being open for extended periods of time (eg. more than an hour). I've even seen the prices stop updating after a while.
2) Often appends a bunch of 0s after the decimal to the price of your order, forcing you to manually remove them in order to place the trade
3) This morning the platform was extremely slow, and I was unable to load pricing data into the charts. I tried to submit a ticket to customer support, but the server was down. I didn't try to submit any trades, but for all I know that may have been down as well. Keep in mind this morning the S&P 500 was down 10%. Nice to know my trading platform will crap out on me when I most need it
4) UI sucks and is confusing. When specifying how many shares you want to buy, you're not told on the same dialog how much total that would cost. The charts suck and are confusing to work with.
5) One day I submitted a sell order, and it ended up buying. Although I was convinced the platform screwed up my order, I gave OptionsHouse the benefit of the doubt and figured I must've made a careless mistake. Then later in the day I attempted to sell again, only to have the platform issue a buy order again and give me more or the stock I was trying to sell. At this point it was clear the platform fucked up my order, so I called OptionsHouse. They basically just told me to use an alternative method in the platform to close out my stock (clicking the Close/Adjust button).
During my call about #5, I mentioned issue #2 (it had been months after I submitted a ticket for it). They told me it was a known issue that they were working on. How long does it take to fix a bunch of trailing zeros after the decimal being appended to your order? Do they even have a dev team? The fact that it's been months and they still haven't solved such a simple yet incredibly annoying bug gives me absolutely no confidence in the future of their platform.
I'm going to transfer all my funds out, probably to IB or RobinHood. This morning was the last straw. Having the platform down when the S&P is down 10% is unacceptable. OptionsHouse used to have the lowest commission fees, but that's not longer the case with RobinHood (although of course you don't get nice things like options trading and a web platform).
https://www.interactivebrokers.com/en/index.php?f=4969&ns=T
It basically imposes a minimum fee of $10 per month. It does gets waived if you have more than $100,000 USD in your account though, so this is just something to keep in mind, and YMMV.
I would personally just go with Robinhood for long term investing. No fees is better than low fees, and the longer the time frame you're investing, the less important individual trade execution and customization (areas where IB excels in) becomes.
RE: Algorithmic trading. Check out Quantopian:
Instavest is the only platform to address these issues in a systematic way.
You'll see high quality investments ideas that have been backed by real money. You can choose to invest in these ideas and have the investment leader notify you when they sell or you can invest in your own idea and share with it with the community.
Our equity trades only $3.49 a trade.
Why should I believe this is something other than wagering on survivor bias?
I know that instavest.com (YC company) is powered by them as well.
If you do long term investments and you are learning and/or want a full package of information and tools: TD Ameritrade and their Thinkorswim platform.
I don't quite understand why the OP wants to do this. Algo trading is mostly about market making it seems - finding a spread and keeping ones risk as neutral as possible. I suppose there is always a market to be found - but I would assume that one would have specific domain knowledge rather than hope to trip over it.
Great link though thanks
Disclaimer: I am a TagniFi co-founder.