Eh...I think I'd lean the other way, and buy the 1.8. ; Then again...I find it hard to justify renting unless we're talking about a lens that costs many thousands and I'd never consider buying it. ; The difference in sensitivity between the two wouldn't quite be enough to not justify spending the extra and buying the 1.8 - you'll get a lot of fun out of the lens. ; (I picked up my version of that lens, the 50mm 1.7, used, which made the purchase even easier to justify. ; I'm looking to maybe add a 30mm F1.4 next to get a little wider perspective, but the 50 has served its duty well).