Super UFO is great for the price but lacks a parallel port.
GD7 is a very good unit and with 64Mb it's even nicer but it does use non smc format for the ROM files and it can be troublesome to convert them and the file naming convention it uses is somewhat cryptic. The price of $185 used is in the ballpark of a new 64Mb SWC DX2 (about $210?) so you might want to consider a DX2.
If it's between the UFO and the 64Mb GD7 I'd go with the GD7.