I've always enjoyed the South Stand more than the others. I always seem to find idiots in the RDU nearby, and the main stand seemed a bit stale and condeming of certain things when all I wanted to do was yell abuse at a certain Hibernian player recently... *ahem* (Well, April 2006, damn how time flies)
In my opinion, Block X is the best. A little bit up, but nae too far, and you can get an excellent perspective on proceedings, while being close enough to hear the players, hear the atmosphere and yell at players without worrying about what you say (Encouraging things... usually), and see them easily. Of course, if you're short sighted like myself, sitting near the front is always a major benefit