The general wisdom is that the model 2 Sega CD is more reliable because it doesn't have the drawer (more moving parts = more likely to fail)
General wisdom is also that the model 1 Genesis is the model to have (for superior sound and compatibility and such)
This leaves you with a very wide Genesis and, if you care about the looks of the system itself, an extra piece to get ahold of that extends the base of the model 2 CD to the full width of the model 1 Genesis. Or you could just put a book or something under it. Whatever.