I have a 9855, the main reason I bought it over a 9835 was because it was compatible with my factory steering wheel controls in my Altima.
The glidetouch is kinda annoying at first, but once you have all your setting done, you don't really need to use it much. I use my remote and steering wheel controls anyways. The 9855 is a really good HU. Before the 9855, I owned a 9813, which was my alltime fav deck.
I think the 9855 looks sharper than the 9835 too. As far as specs, I'm pretty sure they are exatcly the same.