What poker game should I focus on (limit HE, pot Omaha, etc.)

[BluffTHIS!]

Obviously you don't like variance. So you should avoid PLO and short-handed anything like the plague (though if you do learn how to play them well and have the appropriate roll for a given level they will be more profitable long term). But your variance should be less in nl than limit. However the reason you are probably finding the higher level you went to frustrating is that you aren't practicing good game selection. A table full of nl rocks playing only pairs and AK and yourself doing the same doesn't make for a good game. But with accounts on multiple sites you should still be able to find good games if you make the effort.