Standard ESLs work great for silvers. I do enjoy the hairball though. They seem to work very well for kings. Anything with a lot of motion and maribou works good for both.
Alaska: We're all here cuz we're not all "there"
I thought it would have to do with the weight? Most hareball leeches are body weighted to get down deep or help when the current is swift.
MOAL/String/Hareball leach more fun to tie + more action = winner in my book
Though you really can't go wrong with a standard ESL in most cases.