I've tried both, and I thought that limit was the most profitable form of poker. But it's really more frustrating that NL, because there is no strategy to sizing one's bets to deter (or encourage callers). When you have a fantastic hand that's vulnerable, there isn't much to do besides bet it all the way and hope you're not drawn out on. I've switched to No-Limit and although I'm losing bigger, I'm also winning a lot bigger. It hurts when you go all in with kings, someone calls with ace-8, and he makes trip 8s on the river. It hurts a lot more in no-limit, but what you can win with a big hand more than makes up for it (so far).
As far as hold 'em varieties, one of my objections is that almost nobody plays pot-limit online. I suppose it's an in-between form of poker, with far greater risk than limit but far smaller pots on average than no-limit. It requires an in-between level of aggression compared to the other games as well. I'm often looking for a low-stakes pot-limit game but the tables are usually completely empty.
Pot-limit has of course flourished most noticeably in Omaha, where it can generate massive pots on par with any high-stakes No-Limit game. Just reading HighStakesReport on a daily basis, the eye-popping headlines usually come from Omaha, e.g.:
I've also heard that side games at the big tournaments are sometimes played pot-limit because it can generate such juicy stakes with the huge raises and re-raises.