I recommend Tactics for two reasons. It's the better game, and it's cheaper. When you pick up Crisis Core at a later time, it'll probably be cheaper than it is now.
Final Fantasy Tactics: It's a great game. Very fun, great story with nice plot twists and turns. The music is pretty good, and those cell-shaded cut scenes look amazing. There are a lot of stuff to do in the game such as assigning different jobs to your soldiers. There are over 20 jobs to choose from. Each job have their own ability and weapons/equipment. It'll keep you busy for a long time.
Crisis Core: FFVII - It's a pretty enjoyable game. Nice battle system, easy to use, pretty fun. Using materia is also easy to use and you can fuse them to make a new materia or enhance it. The DMW/power surge is pretty confusing. It comes out random at times. I went from level 5 to 8 in just one battle. There are also a lot of optional missions to do, but they are pretty repetitive. Most of them are pretty hard since your enemies start casting death or something. Music is great, but some FFVII classics are ruined. The story is so-so. It's very boring at first, but at around the end, you'll start to enjoy it, especially if you played FFVII. The ending is beautiful and brilliant.
