i have the studio88 fully loaded rocks the shit outta the extreme in my opinion
I have 16mb more sounds (when fully loaded but i can't load the last 16mb only accepts 7 cards so i have the same amount of sounds at one time as the extreme)
Hard disk recording and streaming
a beautiful silver synth =)
Extreme = usb (v handy) and tubes a bit of a gimmick but its there so you gotta use it.
Tritons just depends what you need studio is still flagship (I thought damn when they released the extreme ive been sold a lemon now ive played and read what i have the studio ids defo my choice)
Classic a lovely board only takes 2 exbs rack 8 boards but there are 9 in total studio comes loaded with exb8
The studio hard to come by secondhand atleast here in the uk (seems those that bought it love it and i understand why)
Extreme you might get some kid put one up on ebay
Classic a great bargain second hand
Rack if you stuck for room get a another controller absolute bargain on ebay ( inearly bought one of these as an addition)
http://www.korg.com/gear/series/TRITON_SERIES_COMP.htm
also check
www.irishacts.com
www.tritonhaven.com
Both u will find most peeps talk the extreme (but check the long term users a different story will appear) cos if it vwas new users it would be the oasys but they can't afford just like me so therfore the extreme rocks as the latest pice of kit.
Ps if you do go triton or karma get karmalab Karma triton or karma mw for $100 best buy i8 have in my studio