Stowe and Breck are WORLDS apart!!!! If you have the time and dispendable resources, go with Colorado....my God. If nothing else, since you are an east-coaster, you'll always have Stowe in your backyard. If you go to Colorado, you'll get hooked! I even assume you won't focus so much on the park as you will our just getting able to take-on the big hill. (If you are new, the Imperial chair will BLOW YOUR MIND.) As for the Altitude: I don't get bothered, but I have seen others be put out of commission. If you are in decent shape, then water and rest should take care of your issues.
The conditions are a crap-shoot at either resort. El-nino pretty much dicked-over both resorts, but I think Stowe is a little more on-par with their average than is Summit Co (Breck, Keystone, A-Basin).
You may also want to consider Lake Tahoe. They got hammered this season and have a huge base depth. If it is sunny, you'll get great spring condiitons. If the weather is feisty, there is a good chance some of the resorts will still be getting snow.
Also, on the night skiing....bigger places don't have it because it is expensive. Between lighting the hundreds (Gore/Stowe) or thousands (Breck) of acres and keeping the resort operations going....it often isn't worth the cost. Most people enjoy first tracks as opposed to skied-off evening hardpack.
Traveling the States and Taking Pictures