Is this for your 90 gallon tank? If so, an Aqua C Pro would still be on the small side for that size a tank, but would still be good. If it HaS to be hang on back, then Aqua C Pro would be decent & trouble free, just make sure you keep your bioload low, and keep your water changes and maintenance up!
Is this going to be HOB
or in-sump? What is your budget? If the skimmer can fit into your wet/dry, an in-sump would give you 2010912390128 more options, just FYI
Let us know... the more info, the better