I am a Gary Fisher freak, Right now I own 5, various years and models. The 09 Marlin is a pretty nice bike, but if you can afford the Piranha, you are getting much better components, the main one being the fork. But if you cant go that high in price, the Marlin will do you fine. I had a 07 Wahoo a couple years ago that I loved. I wish i still had it as a spare, and thats a step down from the Marlin. That bike never ever gave me a single problem, not even the Dart 1 fork. And at that time, I was a 260 LBS fat @ss.
The big difference between Trek and Fisher is how the frames feel to the rider. The Fisher frames have longer top tubes, both are sweet bikes, its a matter of what feels good to you. I have long arms, thats why i like the Fisher frames, they work for my body.