Sigh. You are never going to get good answers until you pose a good question.
1. Budget - what can you spend, how flexible is it.
2. Do you plan on using it for anything other than DJ - street, a bit of mucking around on trails etc?
3. By "gears", I guess you mean rear gears. Or do you mean front gears also? There's a big difference. Any bike with a derailleur hanger (the question-mark shaped bit on the right hand side rear dropout with a hole in it) can run a rear derailleur. This is obvious at a glance as soon as you can see a picture. If it's not there, then strike it off your list because you can't retrofit one.