Being new to this and having recently bought my 1st mtb, (stumpjumper) there would be 2 things i'd look at if i had to do it again.
1)- it must have the components i want so that i don't have to replace 1/2 the bike aftermarket. I would look at the components and try and find a balance between price of the bike and what components i'd wanna replace. The higher the $, the less tolerable of components i'd wanna replace.
2)-reputation. again, being new to this i'd have to trust friends who know something about bikes, and reading reviews to find common threads.