Well "pulling data" directly from your database server it's a terrible idea, managing your connections / repositories / dao or whatever methodology your using from your mobile app would be a more challenging rather than just talking to a rest service.
some advantages of a rest service:
- you can put any front end on top of that, that means a web
(javascript front end), mobile, tablet , etc.
- you are reusing your code
- you are using a thin server approach
- you are decoupling your code
- you can send json over the wire, your mobile app will be back-end agnostic, so you'll be able to switch your REST service implementation if you want (moving to another programming language) without refactoring you mobile app
take a look to a architecture design named API first probably by reading that you'll get a bigger picture of what I'm talking about.
performance?
well that's a little bit broad assumption, I wouldn't be too worried about that if you have a good / solid architecture design over a decent relationship between traffic / hardware you will be fine.
I'd suggest for you to take a look on servicestack which is a very nice framework out there with a very nice performance 3.9 is free and from 4.0 is a paid version either way using web API or Servicestack are good options the best that you feel more comfortable.
