Sooooo many to choose from, try and decide what sort of riding you like to do..??
Bike wise you have full suspension, Hardtail or even Full rigid...
Suspension choices can get a bit out of hand..!!
There are plenty of us on here to give you advice..
Find a budget you want to spend and try to stick to it as things get out of hand pretty quickly..
Brand wise everybody will probably say something different as most people have a preference to brands etc
If you have the knowledge I would say build your own because you always get a better bike in the end, but not everyone has that choice..!!
Go to your local shop and have a look and ask questions (not Evanscycles..
my personal opinion)...
I'm sure someone on here will point you in the right direction shop wise..