Well, IPTorrents is a must-have, it's probably the single biggest general tracker in the world, and with tons of freeleech to boot. Everyone needs IPTorrents.
You might also want to go with
SCC, just because of those awesome packs which are unattainable anywhere else on the internet. The drawback of
SCC is that it has ONLY scene content, whereas
GFT has P2P content as well. But
SCC just seems to kick
GFT's ass in all other departments (except pre-times which are roughly about equal)
The third one is hard. On one hand you have Filelist.Ro which is an amazing tracker, and all torrents above 4 gb there are auto-freeleech. It also has a big collection of untouched DVDs and HD movies which you cant find anywhere else. Then there's DigitalHive which is a decent tracker too, with lots of freeleech. Torrentleech probably has the most content out of all general trackers after IPTorrents, and is fairly easy to seed as well once you get past the wait-times. I will personally pick Filelist though but that's just me. Lots of people swear by Torrentleech and that's their choice.