Never tried Kongregate. I've used a lot of game sites, and Armor Games is my favourite, the ranking system is quite nice. Forums are nice. Unlike other sites, it doesn't rely on advertising and games made for movies and stuff *cough*addictinggames*cough*
armorgames is the best site, but its a little slow to update some times. i may go to another site if i get bored (btw: i have playd on armorgames sinces it was called gamesofgondor, i just got to be a member not to long ago)