the bigger the sump, the better you will be in regards to micro bubbles.. I did a 33 gal under our 120 and it could just barely slow the water down enough to let the bubbles clear before getting sucked back up into our display... my vote is that if you have room for a bigger one.. do it.
Side note: If you are using a skimmer and a host of other equipment.. you will quickly find that a 10 gal. is not big enough either and will be harder to work in, clean and organize all your bits a pieces of equipment if that is where you intend to keep them all.