Suunto Zoop--great value and also nitrox compatible. Should you choose to, you can always drop it into a console from Suunto. Some folks don't like it because it's conservative, but I actually like it that way--I like to err on the side of caution since I'm a worst-case-scenario person.
I ended up going with a Vyper Air when I first started because I snagged a really great deal on one that came w/ the air integration at under $700. If you're renting gear, you won't really be able to use the air integration unless you're willing to forgo the SPG since most rentals don't have an extra HP port for you to use. (My worst case scenario self doesn't like that.) Otherwise, depending on your budget, you can always get something that is air integration compatible and then in the future, should you choose to, you can always add it on.
You can always upgrade from the Zoop later on and then make it your backup or depending on your budget you can keep the end in mind. If you know you are going to be going further into the dive world, maybe you want to consider something that also has gas switching, etc. It'll be more up front, obviously, but you won't have to upgrade later.