Late to the party:
When I was a kid I LOVED...both...
But ultimately found Sega CD more accessible. No store in my suburban/rural town carried TG16. I had to drive at least an hour to get anything (which is why I only had a few games for my Turbo). If I could convince my parents into buying a game for me, it would be tough to also get them to drive an hour to scoop a TG16 game, so I more often played Sega CD. Also the Blockbuster Video carried Genesis and SNES but no Turbo.
Now, in hindsight, and multifaceted adult opinion, I vote Turbo CD. I won't knock anything on Sega CD except that Sega should have added video out through the cd, so the Genesis could compete in the "colors on screen" market place. There are many games I love on both systems, but in overall playability, I choose Turbo. The Ys series builds a really solid foundation for me here. Snatcher on Sega CD.
Make no mistake. It's really very close for me, but I think, if we are including all PCE CD titles it's a no brainer. My copies of Kamen Rider Zo, Lunar, and Night Trap are pulling their nostalgia spades though!
Great thread. I've really enjoyed reeading what everyone thought as this is a question I often ponder.