I just went through this with my CTLS (which I pick up on Friday!) The 696 has a battery backup so you can start it up without anything else on which makes it nice to program while waiting for ATC, practice, etc. Also, the GDU 375, although could be "approved" in a CT, they don't bless it according to my set up person. This is merely heresay, but I think they wanted a little more history before installation. They had one in a plane last year and took it out. It does require external antennae also which might look kind of nice compared to the round ones on the dash.
I finally decided to go with the 696 for now and IF they ever come out with the G3X which combines the 375 and 370 with AHARS, magnetometer, etc, I'll just pop out the 696 and use it as a backup and EFB (electronic flight bag). Hope this helps.
John
John and Julie Johnson
Lubbock, TX
N227CT (CTLS)
Wave #5