The XRGB-1 is excellent. It has the highest compatibility of them all. That box will run everything, even the most bitchy pcbs with no problems. Also it uses dials for color control. So if you want to lower the red on the 1, just turn the red dial. On the other models you have to hit menu, scroll down about 20 notches, then lower the red as you want. One button press for each action. The 1 is by far the fastest to actually use. It also has 15khz output (the 2 does, but the 2+ does not).
The only feature it's really missing is that it can't impose fake scanlines. But if you buy an SLG3000, it fixes that issue. And the SLG3000 has much better scanline options then the 2 or 2+. What might be annoying for some people, is that the 1 only uses Dsub-15 for output. Meaning the old Japanese PC plugs. But if you get a boxed 1, it comes with VGA adapter cables. And you can easily get your own adapter cables separately.
I have a 1,2,2+, and 3. And the 1 linked to an SLG3000 is my favorite setup. It's quick, no bullshit, small as hell, and works wonderfully.
The 1 is also the most durable of them all. I've heard stories about the other models dieing, bricking, etc. But the 1 is rock solid. It's also the
cheapest. If you get a chance, pick one up.
The 2+ has the worst compatiblilty of them all. It's fine for console stuff. But for pcbs it's shit.