Which of these are better? I know a bit about Disgaea, but not the others. Do they all look and play fairly similar?
Disgaea is easily the most acclaimed of the bunch but it also the most expensive and hardest to find.
Many were disappointed in Phantom Brave so Makai Kingdom is getting a much better reaction and is probably second to Disgaea in terms of praise. Easy to find since its new but you'll pay full price.
LaPucelle is probably the least acclaimed of the lot but it's also first so the play mechanics are supposed to be much easier to get accustomed to. And it's not hard to find and can be had used for under $20.