Chalk another one up for bullshit bosses, so annoying going up against them sometimes although I have found a few to be tolerable; Chaos (Dissidia) and Hazama (Blazblue CS) to name two that hit that "just right" balance.
Hell bullshit AI in general pisses me off with their stupid turnarounds sometimes. Perfect turteling, instant counters, and then completely destroying you just as you are about to beat them. It can be good practice, but it can also be torture. Some major culprits of bullshit AI I've witnessed are I-No, Sol, Unlimited Ragna, Nu, and some of the lvl 150's in Dissidia.
I-No's computer AI is a stinking whore. I can beat her, but the ***** has to make it an utter chore to do so sometimes.
Sol and Ky are also big douchebags I don't trust with the computer. Sol always ends up blitzing your ass and fucking locking you in a corner or some bullshit. Ky begins to turtle like there is no tomorrow before counter attacking to all hell on you. I can beat em, but they have their moments.
Unlimited Nu and Ragna....FUCK YOU!! ESPECIALLY Ragna. That **** is near broken in his unlimited form. More defense, more damage, permanent blood kain mode, constantly rising heat gauge, distortion drives ALWAYS take priority over yours. FUCK YOU!! BURN IN THE DEEPEST PITS OF VIDEO GAME HELL! Fighting him is the biggest pain I've had to endure in a fighting game in a long while, that **** just pulls out all the stops on you.
Lvl 150 characters in Dissidia's duel Colosseum, pretty much what I've just ranted about and add "WTF one hit and I'm in break mode!? FUCK!!!"
As for finding a main, well that's never been a big problem. I tend to try a bit of everyone when I start a new game and see who I get most comfortable with. I try to main at least 3 characters, 1 MAIN, a secondary, and a tertiary character. I don't like being confined to one single character. Hell Half the cast in Dissidia I can flawlessly use...but then again I've sunk 500+ hours into that monster.