Fat Princess is definatly my favourite by a long shot, indeed her aerial game is key, by jumping in and out weaving planting bombs and using Forward Circle throwing the knight down is great, the knight also knocks them to the floor ready for more combo happy sqaure,sqaure, up sqaure, jump up triangle for instance..and if the knight doesnt hit i swear it leaves them in abit of block stun so as your throwing it at them jumping in you have time to make your move.
To get in on kratos i usually block his attacks, dodge and sqaure,sqaure him and follow up. or block and short hop doing neautral triangle then follow up by attacking or throwing. But still he can be annoying indeed. and i do agree her meter doesnt build too fast maybe abit more perks in that department.
Just played my first game as Fat Princess then so I'm not the best judge but she seemed kinda fun. All of her triangle attacks seem to work great, especially for arial play (as someone else said).
I found all her O stuff (The summons) a bit useless though, I'm guessing there's a trick to it and it just takes some getting used to but I think I'll stick to Sly. They did seem interesting though, I just couldn't seem to get them doing any real damage.