I enjoy both series quite a bit. If you've already seen some of TNG then I would suggest watching all of Enterprise, because it is shorter and will take less time. After that you can move on to TNG!
I like both. Here's my honest opinion: The first two seasons of Enterprise are often terrible, it's third season is my favourite Trek season ever (it's cheesy, but a good cheesy) and the fourth season is pandering TOS fanwank. Unless you're a die-hard fan you often won't have a clue what's going on. The finale is an awful TNG holodeck episode. TNG is slow-paced, early-90's ultra PC fare. The first season is awful, and it's often bland, but it has some great episodes. Some of it's ideals are dated. Some episodes are utter garbage.
^ It actually is. He/she posted it here, then posted it in GTD. Farther up the thread, Ice said it could stay here.
ENT, just to be fun. If you're more used to watching contemporary TV and don't have an emotional investment in TNG, it might be easier to get into.