I have a RRA Tactical Entry AR that has a 16" barrel. I've been looking at different optics and reading most of the post. I plan on shooting this rifle no further than midrange. So what optic would be the best?
Hell, some people think that anything beyond 100yds is "long" range! Who knows what "midrange" means?!?!
sobrbiker gave you some good advice...don't try for one, jack-of-all-trades setup with your AR. It is better to have one rifle (or upper) setup for an ideal shooting situation that best meets your needs in that situation than it is to compromise and have one rifle setup to do many things...none of which is the rifle equipped to do really well.
That said, 99% of the shooters I see do well with an AR equipped with a traditional optic with a variable power range of 1-4x. That gives you close range shooting ability in addition to the ability to extend out to longer distances (depending on your skill set, ammo, etc.). If you have the budget, the Nightforce 1-4x24 is an excellent scope in that range with all the features you could ever want in a scope that will last a lifetime and work when you need it to work. Same with the S&B Short Dot scopes. If you need a more budget-minded scope, you might look at the Burris XTR 1-4x24 or the new Nikon M-223 1-4x20.
It really all comes down to you and what you might prefer. The best advice I can give you is to try out different optics. If you have somewhere like a Cabelas or similar retail store close by, or you have any shooting buddies with rifles equipped with options you are considering, take a look at them and see what you like best.