i have lived near mammoth (in tahoe) and i am currently riding whistler...mammoth's long seasons are all dependent on what the entire norcal weather is doing...a couple years ago the upper mountain from mccoy station was open until july 4th, and they made a small effort to keep their parks going, but a lot of people don't know that passes that are good at mammoth are also good at june mountain, which is 15 minutes away and is well-known for parks and comps, too...plus if you live at mammoth you are also 2.5 hours away from tahoe, including some great skiing at kirkwood, heavenly, squaw, and good parks at northstar and alpine...mammoth is also very high in elevation, and has huge setups (that don't require a XL pass)
whistler is definitely better with glacier riding, not to mention there's a lot of sledding in BC if you have yourself a snowmobile...both mammoth and whistler are Intrawest resorts, so if you're looking for a job, i'd definitely apply with Intrawest (what's your degree?)...the nice thing when you compare whistler and mammoth is that whistler is twice as big as mammoth, although mammoth is still huge...whistler also has that great BC heliskiing that mammoth lacks
although i haven't ridden anywhere in colorado, i have been to vail and breckenridge during the summer, and everywhere it seems to be an entire tourist trap for rich people, so i am not sure if you really want to live there...i don't think vail, keystone, and breckendridge have long seasons, either...it is also about a two hour drive from any major city (denver methinks)
unfortunately, i can't tell you anything about utah except in mid-winter the snow is great and the parks are good, too