where are you going to ride it most? if it's basically a park ski but every now and then it'll be on groomers (so like 90% or more park) go with center...IT DOESN'T MESS UP THE SKI, I don't know why but people always seem to think that if you center mount an AR6 it will make the ski explode or something, I center mounted my 09's and they were dope in the park and pretty good out too. However if you plan on being out of the park (somewhere around 50%-50%) I'd recommend -1.5, from what I've heard, that's best. If it's basically a groomer ski that sometimes goes in the park, then go with -2.5 (but I'm guessing that's not the case cause you didn't like it there before).
~WAKIN' UP THE NEIGHBORHOOD TONIGHT!~
~I could carve off a jump so hard I'd come in forward and take off of it switch~