semi dub post but i want to try and actually help, and i grew up skiing sugarbush, so here goes:
in terms of sidecountry it has to be some of the best in the east. i've never skied anything better than what sugarbush has to offer. i haven't skied everywhere in the east (no stowe or jay peak as the two major ones i've missed), but i havent seen any sidecountry better than what sugarbush has. in comparison, killington and sugarloaf both seem almost childish next to sugarbush in terms of trees and things. MRG is also going to be better on a good snow day, cause its MRG. and obviously its right down the road so an awesome option for any really good days after a lot of new snow. to try and put some context on it: i have a friend who grew up racing at killington (and before you get into the racers are douches thing, he's one of the nicest kids you'll ever meet, and from what i could tell, all the kids he raced with also seemed like decent enough people) and a few years ago me, him, and another friend went to ski there for a couple days. typical new england skiing, not great snow, and everything was getting skiied off well before the day was done, it was still fun at killington but certainly nothing to write home about. after that me and the not killington friend went to sugarbush for a day. same type of snow conditions, but we spent almost the entire day skiing trees that aren't marked as glades by the resort, found good snow in there the whole day, and had a blast. my friends said hands down sugarbush was more fun and some of the best eastern skiing he'd done, and, terrain wise in the trees, as good as anything he'd done out west (he didn't grow up on the east coast and learned to ski out west).
only real parks are on graduation and riemergasse on mt. ellen. graduation park is smaller for less advanced park skiers and riemergasse is bigger. they put features up sometimes at the base of lincoln peak, but never anything big and no jumps. jumps aren't quite as big as other places, but normally kept in good condition.
in terms of passes. if you qualify for 420's (ha) do that. its full mountain for around 300$. the only legit place i can think that might come anywhere close to as good a deal is saddleback. if you don't qualify for 420's then honestly i'd say you'll probably be plenty happy getting a mount ellen only pass. my house is closer to the lincoln peak side so i start there and spend a lot more of my time there than mt. ellen (not to say mt. ellen is worse, i love it every time i go over there, read on). the slidebrook chair is awesome and fun to ride, but it does take around 17 minutes and closes a lot due to wind and cold because its so long and exposed in areas, and if it's closed taking the bus back and forth just isn't worth the hastle. the terrain is good enough on either side that waiting for the bus and riding it over isn't worth the time. the only thing you'd really be missing on lincoln peak is castlerock and heaven's gate. castlerock is awesome cause its castlerock and heaven's gate is awesome because of the trees off of paradise (and also organgrinder and jester, but not quite as awesome as paradise), and you can always buy a day ticket if you ever get the urge to explore lincoln peak for a bit.
sorry that was so long, but hopefully it helps answer your questions pretty well.
sparknotes:
sugarbush sidecountry: awesome, as good as pretty much anything in the east, or better.
sugarbush parks: on mt. ellen, good.
sugarbush passes: get 420's if you qualify, if not you'll probably be happy with just mt. ellen pass unless you really aren't concerned about the money and want the full mtn.
