I've used them all. Pretty good once you get used to the control scheme it uses on the screen. If you have big hands like me, it can be a pain to play with them. Download and try them out, there is lite versions!
I've used SNESoid and NESoid. They work pretty well, but I also got a little frustrated with the controls, it took me a while to get used to it. But overall a fun way to play games.