I'm assuming that being an "ass" means that you're not particularly bright or clever, and being a "jackass" entails being, well, an obnoxious, inconsiderate curmudgeon. If that's the case, then I'd take being an ass any day-- there's nothing morally objectionable about being a bit slow on the draw, after all; there is, however, a
lot wrong about being a prick. At the end of the day, I'd prefer to have a clear conscience-- no matter how simpleminded that conscience (in its rationale and justifications) may be.