Paypal: Used it for years without any problems so far. As buyer and as seller.
Dwolla: Registered an account several weeks (months?) ago. Didn't use it since then. Today I've tried to log into my account and it seems that essentially the account has been locked and I'm required to upload a photo ID in order to get my account unlocked.
So it seems that other payment providers aren't really better than Paypal. I'm glad I don't have any money stored on Dwolla - let's see how they handle the situation.
when you enable international processing fraud rates spike (double-digit percentages in some countries) and you end up building an agressive fraud protection scheme like PayPal have
the new startups have the advantage of only serving a relatively small less risky market, and being obscure enough not to be a target of fraud groups
these new startups have nice features such as simple API's etc. but I haven't seen anything yet that is revolutionary in terms of technology that will break out of the fraud/blocking cycle
Edit: to add, I am not being dismissive of the new startups, on the contrary I am using Swipe on a new product, and I really do hope that one of these guys nails this space