Well, both available kits have good and bad points, and it is said that modelers who can afford both kits should do so in order to pick certain bits from one kit and others from the other kit to get the best of both world.
The Monogram kit (which I have) is very decent. The only 'major' problem is the size of the cockpit windows (oversized). It's got lots of bits for the cargo bay (which I tossed away, anyway, because they were a bit too crude for my liking. The Revell kit is decent too. The problem with that one is that it comes with a raised tile pattern that is way overscale and that needs to be sanded off.
Both kits can benefit from the now numerous aftermarket sets of parts and decals available: cargo bay update kit, new main engine exhaust cones, decals for tiles, old or new NASA markings, masks for painting the different types of white insulation materials,...