i have never used pellet hops, and never will, because i have some inexplicable attraction to whole leaf hops. Beyond pellet/whole hop ratios, (which should basically be an alpha acid content difference, and can be measured accordingly,) there are also some other factors, mainly freshness and volume. Pelletizing hops is great for many reasons, from what I hear, including the smaller amount of space needed for storage, but they can stale faster as well. It is certainly a matter of storage, and how quickly they are used, etc., but I like the idea of using unprocessed, fresh (dried, but not old) hops in my beer. Pelletized hops will also break up almost immediately in a boil, and can clog/coat equipment more so than whole leaf cones.
good luck and cheers!