As for the bikes, well, it's a close call. The Trek 4500 WSD ($500, www.trekbikes.com) has an aluminum frame, Judy TT fork, a mix of Shimano and Bontrager components. Very serviceable setup for an intro mountain bike. The Marlin ($520, www.fisherbikes.com) is basically identical—aluminum frame, Manitou fork, a mix of Shimano and Bontrager parts. It's a little more aggressively designed, though, with a slightly lower gearing to accommodate big, steep hills. If the Marlin you saw had disc brakes, then that's a retrofit of some sort, because they don't come from the factory that way. Disc brakes are a good thing if you ride a lot in wet/muddy conditions, as it's then that they really shine. They also don't wear out rims like cantilever brakes will over time. Otherwise, it's a bit of a wash.
My sage (and wholly predictable) advice, then: I'd ride them both and see what you think. A women-specific frame is indeed an advantage, so that's a point in favor of the Trek. But you might find that it's not a big deal, in which case I'd go with the better shop and the Marlin.
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