A 29 or 30 gallon could house two angelfish but that's really only for breeding setups, a full grown angel by itself would probably be fairly cramped in a 29, not saying you couldn't do it, but I'd never put my angel in anything that small. The 40g would be the best option out of the two, a 40b would give enough horizontal space but keep a thin substrate so they can have the most headroom they can