Honestly I think you should go for the Duo R. a LOT of the US games are actually more expensive than the Japanese imports, Also the CD games shouldn't be passed up. Also there were simply a whole lot more games released in Japan. The best of both worlds would be a Duo R with a mod to let you play American Hu cards.
I got one for $150 (Unmodded) not long ago. It has a teeny scratch on the lid but is nice and white. IMO the system is well worth that. I didn't blink to pay $200 for my second Turbo duo a few years back from TZD (before I knew about the capacitors) because It's my favorite system ever. I always regretted selling my original.
As for the TG 16, I never really regretted selling mine (with Turbo Booster) IMO The PC engine is a much more elegant machine.