I used a 10 for my QT since I only had little fish going in to my 40. I had a small HOB filter on it for aeration and filtering (I used floss instead of cartridges for frequent change-out) with a heater. Nothing else needed.
On a 29, I'd be you could also use it for a sump just fine.
Edit: I have 4 or 5 tanks around here for misc purposes. All are 10s. I have a 10 fuge, few for QTs, and a couple spares for whatever purpose. For whatever that's worth.