Which mountain bike should i choose?

I'm thinking about either:

Trek 6000: http://www.trekbikes.com/us/en/bikes/200...

Diamondack Response Comp: http://www.diamondback.com/items.asp?dep...

Gary Fisher Marlin Disc: http://www.fisherbikes.com/bike/model/ma...

I'm on a limited budget.

I'd definitely go for the Gary Fisher. firstly, if you check them by the looks alone, Fisher owns them all because it looks more professional and serious, despite what others say- Trek looks simply cheap and not serious, and the Diamondback is more like a dirtjumper.
Trek manufactures some cool bikes but not this one. It just LOOKS cheap and I bet- feels cheap. the components are fairly the same though, so go check out each bike, ride them, because every bike has different feel to it, you may want one and would hate the other, it's personal.
Gary Fisher is totally top-notch, you might not agree but as a pro I say- I've tried lots and they all feel mint, they feel very rigid and durable. they've also stood out tests much more than Treks- it's a fact. don't get me wrong, mate, I like both brands almost equally but in this case the Fisher looks way better. the colour alone, the geometry, everything. you can't impugne that :), this is what a good Trek bike looks like http://www.trekbikes.com/us/en/bikes/200... and I say- Gary looks closer..
but buy whichever you feel better on!
also, if you're more into jumping and freestyle riding- you may consider the Diamondback, if you wanna hit some sick singletracks and do some XC- go for Fisher, this Trek would feel more like just a spare-time bike

happy ridin'

All are fairly equal, go with the dealer you are most comfortable with.

I think the TREK looks really slick! Especially the black! Gary Fisher is also nice. Both have different geometry's, so you better take them for the a test ride before you decide. Also TREK owns Gary Fisher and they both offer a lifetime guarantee on their frames!! The DB looks more like a Dirt Jumper bike and it does not look as slick as the TREK. Just my opinion.

Kimber

i have ridden the marlin before and it is a sweet ride. the new trek geometry is supposed to be pretty sick though. try them both and see which you like. also if you are on a limited budget sometimes you can get the year priors model cheaper depending on your local shops. for my own personal choice i love cannondale. you might want to check out some of their stuff. its a little more but worth the extra couple hundred.

Those three are priced the same? I would buy the Trek if the answer is yes. Ride them all before you buy. If the Trek feels right, it would be the best deal and I too have to agree it wins in looks alone.

Other respondents say the bikes are equivalent. Test ride them all. Pick the one that fits and feels the best as long as the bike shops have good reputations for support.

HTH

All three of these bikes have similar components and should give you several years of service. The biggest difference is the Diamondback has a bit more suspension travel than the other two.

I really think you need to get on all three bikes and ride them. By ride, I don't just mean take it for a 10 minute spin around the parking lot. Have the shop adjust each bike to your size and go ride it for an hour or more. The bike that is most comfortable is the one you should buy.

As another respondent pointed out, if your shop has one of last year's models left over, they'll certainly be willing to make you a deal. Good price or not, you still want the most comfortable bike.

Hope this helps.