I've worked on anvils ranging from a 47# colonial to a 560# trenton, and just about everything in between, my favorite weight range is the 200#-300# for general blacksmithing work, with as much face as I can get in that weight, and I'd say about 100#-150# for knife work with as compact a design as can be had. The one thing I want in an anvil for making knives; crisp edges! For general blacksmithing work, I've got the first inch of my anvil crisp, and a tapered radius from there back to the heel, for bladesmithing I've got the entire edge crisp all the way back. I do very little bending when forging a blade, but lot when doing general work. (Yes I have multiple anvils in the shop) the rounded edges allow different radii to be imparted to the bends I make, but the crisp edges allow me to forge my bevels better.
Hope that all makes sense, and might be useful
Tony