This is kind of a wierd queston, IMO. They are the same console with with only differences being:
1) Terrible orginal TG-16 design. Huge, black, and awkward. The stupid flimsy shell thing covering the expansion bus will not stay on the back, and adding the CD just makes a huge t-shaped thing. The same can be said for the Supergrafx w/ Super CD combo I guess, but considering that set-up is way more capible, and virtually nobody has it, I forgive it. The Turbo is litterally twice as big as a PCE just because they thought (probably correctly at the time) that Americans like stuff that is big for no other reason that it being big. Considering the subsequent popularity of SUVs, I'd have to say maybe they were onto something, but that shit doesn't appeal to me.
2) Pathetically small selection of games that are more expensive, and have super crap covers.
3) Virtually everything for TG-16 is harder to find than PCE.
I don't see the appeal of the US stuff now that things have changed so much. Sure, I had a US Duo back in 1992, but that was when the JP systems were $400-500, even the crap games were $60-100. SFII was $120. The Arcade Card was $130. Now you can get tons of PCE stuff for very very little cash.
I think the TG-16 is just for people that like spending more money, and getting less. The TG-16 only has a two button pad, and Fighting Street is (I think) the only fighting game for it. There is no Arcade Card, no Strider, no Sapphire, no Ys IV, no Dracula X, no Bomberman '94, no Fray, no Macross. Most of the shooters are Japan only too. Bazaar de Gozaru...TG-16 people don't have Bazaar de Gozaru. So sad.
I have the US versions of the Duo pack-ins, as well as GoT, but that's about it. I'll take a $3 copy of Gunhead over a $15 copy of Blazing Lasers any day.