No - if all you want to do is play 68K games, the Duo isn't a good choice due to non-standard resolution (640 x 400), terrible keyboard (it really is) and lack of expansion options (2.5" SCSI drives, hard to find RAM if yours has little).  The Colour Classic is versatile machine, but again you're limited to low non-standard resolution.  I'd suggest looking out for an LC475/Quadra 605), which is small, you can plug it into a modern LCD monitor without issue, and cheap to upgrade.  For B&W only games, an SE/30 would be a good choice, partly because of it's 1.44MB drive.  A Plus/SE with 800K drive takes too much work to get software onto it.

Also consider a later PPC Powerbook (not as many 68K games will run due to compatibility issues, but there are of course many PPC-accelerated games), which can give you PCMCIA (invaluable getting games you've downloaded online onto a CF card, then CF-->PCMCIA adapter).  Something like a 3400 is pretty good - it'll run 80% Mac games, PPC included, nicely.