Tips on buying a beginner mountain bike
At your level all brands are equal and you can find a suitable bike for yourself in almost all brands. Focusing on a specific brand will only make it easier for you to choose but don't, for one second, believe that you've found a better brand than others.

I suggest visiting a couple of LBSes (local bike shops) to get more info and test ride a couple of bikes (even in the parking lot). Pay attention to sizing. This is something that your LBS will help you with.

If you need a bike for getting stronger and having a bit of safe fun then any $1000 26 inch XC hardtail with 100mm front travel will do the job. The bike will take you anywhere and will last for decades.

If you feel that at some point you'll want to get more aggressive then you'll need a more aggressive hardtail with slacker head angle and around 140mm of front travel.