If you're unsure I would probably go with EIGRP. Unless you are sure that your organization will be growing rapidly and you will eventually have a fairly large network. EIGRP is a little easier to configure, but OSPF is generally considered to be more scalable. Also, if you ever buy a non Cisco router, EIGRP won't work with it, although you can always redistribute to other protocols.
If you choose OSPF, I would definitely recommend reading up on it and doing plenty of practice with it. It can be quite tricky with its many different types of areas and such. Also, I hope somebody will correct me if I'm wrong here, but I believe EIGRP converges a little faster than OSPF, although there is not a huge difference like there would be when compared to RIP, for example. OSPF also requires more CPU utlization than some other protocols, although with your current setup, it sounds like that probably won't be much of an issue. Just something to consider as you grow.
I hope I made at least SOME sense here. Good luck.
