I don't really know a lot about the '1. From what I know it's pretty solid, but might not work on some kinds of video inputs. It might be good to see if you can find any information about people using it with RGB-NES or PCE before buying it.
It is supposedly really great, but lacks scanlines (SLG3000 fixes that). It also has no firmware (dipswitches), and not alot of people use it really anymore. I'm focusing on and probably getting a 3 through a trade.
The 1 is smaller/easier to use since its not menu based, but lacks support, from what I understand. So if I have a problem, I am boned.