I have a VPI Classic and the Marantz TT-15s1. I like them both, but the VPI is clearly a better turntable both sonically and in build quality. As for VPIs using MDF...well, what else would they need to use? It's an excellent damping material. The Classic uses an even larger block of it, with a steel plate on top, and it's about as solid of a sounding turntable as you're going to find in this price range IMHO (haven't heard a GT-2000 but part of my love of the VPI Classic is its arm). I'm currently running a Benz Glider on the VPI and it's a wonderful matchup.
The Marantz is a nice turntable but the motor seems pretty lightweight...I like a bit more torque in my turntables. Its not rigidly mounted like the classic and it's just kind of non-reassuring when you go to turn it on and the motor is just sitting there, moving a bit every time you touch it. This would also apply to the Clearaudio Emotion I suppose, they're very similar turntables.
I've heard the Clearaudio Concept at length and have thought about trading my TT-15s1 in towards one. But the Marantz sounds very nice. It just lacks the 'weight' of the sound of the VPI Classic. The Classic digs deeper and hits harder. It's speed stability is rock solid, too. The UniPivot takes a bit more care in setup but you get used to it quickly and it works very well.
Good luck. I don't think there's a bad turntable in your list...just that it might come down to personal listening impressions as well as whether you like the look and feel of the turntable. One of the reasons I like my Classic so much is that it just feels SOLID. Everything is locked in place and there is no tweaking. I am not a fan of tweaker-tables, for what it's worth, like LP-12s. Just not what I want to be worrying about..I like to buy, set up, then listen listen listen.