You can't go wrong with either.....
If you're more of a fan of Hogan and the bigger type matches, than shoot for the WWE Championship DVD. It has some of the greatest matches ever in Foley-HHH , Angle-Benoit, HBK-Mankind, Austin-Rock, and Rock-Taker-Angle. It also has more misses than the others IMO, with a few bad clipped matches, the Ironman, and the Summerslam 2000 Triple Threat (WHICH IS GARBAGE).
If you like the NWA or WCW, get the WHC DVD, and it's a no-brainer there. Plus, you get one of the best WWE matches ever in Angle-Taker, so it's all good in that department. I'm a fan of the lesser known matches of the set like Flair-Steiner.
The IC title AGAIN has one of the best matches ever in Savage-Steamboat, but since it was the 'workhorse' title, you get a ton of better worked matches than the other DVDs, and less "sports entertainment". Tons of great old school shit on there, Santana-Savage fucking owns hard and I adore it.
Once upon a time I was asked by an individual looking to start a Wrestling DVD collection what DVDs they should build their collection on , and I said the WWE/WHC/IC DVDs, simply because they're a great centerpiece full of great matches and fantastic moments.