I agree with most people here that A is the better choice on paper.
Your comments on B seem confusing to me. Options are typically granted with a strike price of whatever the 409A assessment of the fair market value is at the time of the grant. So if they already raised a C round, the ship has sailed on the "Series B" strike price. Anybody who tells you otherwise is probably either lying or misinformed.
So, what you're getting with Company B is more options with a higher strike price. Keep in mind that the strike price is what you pay to purchase the stock that you may then sell at market price. There are also taxes due at exercise. Your net profit from options issued this late in the company's journey, after a liquidity event, is likely to be small because the strike price is so high and the company has already achieved much of its growth prior to your grant.
For instance, if the company IPOs at $15 and your strike price is $7, figuring the fully loaded taxes to be around 40%, you will only make ($15-$7)*0.6=$4.80 per share. To get a more realistic expected value, you should also assign some probability your company will never have a liquidity event or will but under unfavorable circumstances that render your options worthless (e.g. after a down round of financing). The market value of your options during the liquidity event needs to be several times your strike price for it to become a very interesting amount of money.
I recently went through an IPO with my company. The options I vested over four years are about $60k in the money. I count myself lucky that I'm seeing any money at all from them, but really I would have been better off to jump ship a long time ago to a BigCo with RSUs that offer a more certain return.
If you really like Company B, tell them the going rate seems to be what A offered as base. With their recent funding, there's a good chance they'll bump you up if it seems like you're going to go with the other company.