I've tried Overwatch and Saver, both of which I highly recommend. I never realized how much junk built up in a game file and Overwatch cleans it all up every sim night. The games where I use it run much better because of it - very little lag or freezing at all.
Saver is kind of a mixed blessing. It is a pain to have to stop and save every 30 minutes when everything is running well, but the first time my game crashes and I've only lost 30 minutes of game play I know I will be really happy. It's well worth the minor nuisance.
I haven't really dabbled with any of Twallan's other mods, although I'm thinking of installing ErrorTrap in my games with mods. I'm a little bit leary of adding too many mods too quickly, so I'm really just looking for a few key ones that will address the numerous bugs and glitches that EA hasn't gotten around to fixing yet.