i own a sa1620, which is the predecessor of the sa2020 (it was discontinued a year after it was introduced) and have owned a sa2020. the sa1620 is a pretty decent guitar. the main difference is that the 1620 is bolt on while the 2020 is a set neck.
fretboard radius was actually a lot flatter than i thought it would be (i was expecting something that felt more strattish, or more like a js1000 neck), but the neck is fairly thick and wide. the 1260 also is a H-S-S configuration while the 2020 is H-H. but on to the differences.
well the 1260 is a japanese prestige while the 2020 is korean. supposedly, the difference should be minimal, but the 2020 i owned was just a crappy guitar. it had no resonance whatsoever...sounded like the strings were attached to a broom when you strummed it. plugged in, the tone was even worse. the dmz/ibz pickups in that guitar are horrible, or the construction of the guitar is poor. i didn't like the feel of the neck either. needless to say, i jettisoned that guitar on e-bay with a quickness and luckily found a 1260 a few months later. the 1260's
bridge pickups doesn't sound that great, but the single coils (especially the neck one) sound fantastic and tubular. i figure it will be a great guitar with a new bridge pickup. most importantly, it sounds much better unamplified and just seems to be more solidly built.
the at300 i have yet to play. but i live in dallas and see andy on a fairly regular basis, so i can at least tell you what the guitar sounds like in the hands of a master. it is amazing. i can't believe how versatile that guitar is. truth be told, it looks almost identical to the sa1260 (which is why i bought it, the poor man's at300 if you will), but i know that the neck is completely different. the body is pretty much the same, both made of mahogony, although it could be that better cuts of wood are used on the at300. same pickup configuration, but andy has a specially wound dimarzio in the bridge and i think the neck and middle singles are dimarzio cruisers. this guitar has a decidedly vintage meets modern sort of flair and it can handle pretty much anything from authentic blues to high gain rock (but probably not the heavier metal stuff). i've been watching for them on e-bay on a regular basis, but they are hard to find.
the sa260 i have not played, so i can't give my review of it.