The clarion has the most processing abilities. dont know about their reliability. But they have time alignment, the ability to go three way and has 6 volt pre outs.
The kenwood has the second most capabilities, not sure if its 3 way but it has time alignment which is nice if you're going active.
The pioneer is good for the money, but falls short in sq capabilities. dual usb is pretty sweet though.
The 5100 lacks general features and is pretty unfriendly to use. same format as my cd7000, but has way less features. other than a strong pre out voltage and nice guts inside, this unit offers nothing compared to others on the list.
the alpine has good user features and has blue tooth which is nice, but lacks sq features unless you get the imprint which will cost extra. I never understood why the hell alpine is sticking with 2 volt pre outs....
but yea i would choose clarion first then kenwood second....good luck with everything