How do Columbus and Centential hops differ? I have used them both in the past and usually in combination. But I may purchase one over the other in bulk soon.
Which one of these comes out less harsh as a bittering hop?
They're both good dual purpose hops. The Centennial has a lower AA% at 9-12, versus Columbus 14-16.
I think your best bet is to brew two identical beers, one using only Centennial and one using only Columbus, then do a triangle test to decide which you like best.
(Triangle test: someone puts two of one beer and one of the other in front of you without you knowing which is which. Your job is to try and pick out the one that's different. If you can't, pick whichever hop is cheaper. If you can, pick whichever hop tastes best to you).