Here's my view on all three versions....
Vista Jagmaster (1997-2000) - Basically a MIJ Fender Jazzmaster with a Jaguar neck and a Strat Bridge, and 2 humbucking pickups. The sound, feel, and construction quality of these guitars is the best of the three in my opinion. Very rock solid, stay in tune pretty well, and have a nice choice of colors as well (Sonic Blue being one of them). These are getting harder to find now though, and that's rather surprising.
25.5" Scale Chinese Jagmaster (2000-2004) - The 25.5" Scale tightens up the sound a bit, giving it more of a metal tonality than an alt-rock tonality, also, the pickups seem just a shade hotter with less midrange in the sound. The strat vibrato used is a 2 point vibrato unit (usually, I've heard of 6 screw being used). I prefer the 2 point with American Standard style saddles to the 6 screw version for tuning stability reasons. Had some awsome sparkle color variations that you can't get on any other version of the series.
24" Scale Chinese Jagmaster (2004-present) - The only real differences between these and the previous in the series is the neck, which is now a 24" scale converstion neck designed to fit a guitar routed for a 25.5" scale neck. That means finding aftermarket necks for this thing is next to impossible. Seems they improved some of the hardware, but the one I bought did have lots of tuning issues and potentiometer issues (tone control shaft came off with the knob, it did not break, the WHOLE SHAFT removed from the wiper contact and came out of the pot).