Ignore the naysayers - clones can be worthwhile, but not all are built equally.
The best dual NES/SNES clone is the RetroDuo - but depending on the revision, you might have to do some minor minor soldering to add in a small audio dampener to make NES audio sound correct.
Check out my video review of it.
http://www.youtube.com/watch?v=bDJBY9PWqTk
If you want a Famiclone by itself and already have an SNES, the absolute best clone out there is the TriStar/Super 8.
http://www.youtube.com/watch?v=BO5ICApvVNY