I use 9s on a Dropped D tuning on 25.5" scale. the feel is so right for me specially executing vibratos. I tried a set of 10s recently but I still prefer 9s
my verdict
thinner gauge: more comfortable to bend, warmer sounding, more playing time for me(hindi masakit sa kamay), mas ma chug
heavier gauge: more effortless alternate picking, brighter, less playing time for me, tighter on lows(less flub)
overall it's a matter of preference.