If you're going to collect, get the Model 1 Sega CD. If you're going to play stuff, get the Model 2 Sega CD because it is a lot more reliable.
Like at least 3 times a week there are people posting on Sega16 about how they just bought a Model 1 and now it doesn't work and can someone please fix it. The Model 1 is a very nice looking system, and I own and have repaired several of them, but for my playing setup I have a Model 1 Genesis with no TMSS, a Model 2 Sega CD, and a 32X for jailbar filtering. Plays and looks great, plus the vertical space needed is a lot lower than the stacked set.
Just my 2c on the issue, and I play a lot of Sega/Mega CD games.