I know that SUPER has a stupid UI, but it has given me the best results for my videos so far. Maybe I'm stupid, but I can't get Handbrake to do a successful conversion. Always something going wrong
Following the instructions from the first page for SUPER, I've not had any laggy videos or anything. I guess sometimes that could happen if there are too many background applications running.

DivX on the other hand is a nightmare. Smartmovie can't play any video I throw at it. Lags horribly...