Before you buy... whatever you buy...

Familiarize yourself with the different grades of aluminum and what "butted" means since that's what you're probably going to be on.

Familiarize yourself with the different grades of Shimano components since that's what you're probably going to get.

The reason being, all of the frames at this price point come from the same places... So, a 6061 double butted frame form one brand is no better/worse than any other brand. The same goes for the components.

Just buy the cheapest one with the best components you can find.