I have had a 4 channel set up with the 2 rear channels bridged to the sub (Rockford amp).
It was decent but like Ben I wanted a little more so I dedicated one amp to the sub and used the rockford for my sound stage. The second amp I used was a large pioneer.
As I liked how this sounded, it was for sure a more labor intensive install and took up more space. I had to get a distroblock, make sure I did not introduce a ground loop, and run 2 rcas (neither of my amps could be daisy chained).
I also had to run larger power wire, and upgrade my big 3 (I will do those again however).
This system was my best one yet, but it didn't look oem, and took up a lot of space (in a truck at that). I won't do something that large ever again because when it got stolen I was almost blinded by rage, and I don't need that stress again.
I would still say if you are going for compact oem look a 5 channel, and a 10 with some good components will be great. But really it depends on what components you get, and how creative you feel like getting with the install.