I've always had a soft spot for the model 1 with the built in headphones. You seem to get better sound direct from the hardware, but it does make setting it up with the mega cd and 32-X more fiddly. The model 2 is neater in that regard.
I thought the laseractive was supposed to have the best picture as I thought it had component video outputs, but, although I don't have mine yet, it doesn't appear to be the case. Do the wondermega's and the multimega's have better video? What about the terradrive and the megatech arcade board?
The Nomad is alright, but the screen does suffer from ghosting and blur. I did appreciate hooking it up to my tv to play sonic 2 in full-screen 60Hz NTSC for the first time. PAL sucks hairy balls.