The good news is that you can fly direct from NYC to Vancouver. It's a long flight {six hours}, but if you've checked out options, flights with layovers can add the time up considerably. My preferred plan is to try to get to Vancouver as early in the afternoon as possible. The transfer and drive to Whistler takes, in our experience, longer than planned. I think three hours.,
If the weather is nice, the drive is just spectacular. So, depending on how much you want to spend to get there, there are plenty of options. Bus, to a Suburban with driver. You do not want a car while there. You also want to pay attention if you are driving. And the weather can be unpredictable. I know some people who do zipcar. I wouldn't.
On the way back, you can ski half of the day, down to Vancouver, spend the night, fly home the nexf day. No way in hell will I ever fly on a red eye that far, even in the front of the plane.
Keep in mind, Vancouver is expensive. So with the current exchange rate, might be the time to do this trip. I say that preferring Aspen. Canada is affirdable.
So, flying out of NYC is a plus.
Aspen is one of the few ski towns that I would fly into, but I don't love the Denver to Aspen flight. I'd check out flying to Chicago, and Chicago to Aspen. The airport is right in Aspen. You do not need a car in Aspen. First time there, I would stay in Aspen. The bus service to get to Highlands or Snowmass is great. Everybody uses it.
You could fly into Denver, and depending on how we are paying for flights, we do. Southwest, for sure. Then it's a hike to Aspen. I drive in a lot of heavy traffic and crappy weather, but I'll never drive I-70 out of Denver on a winter Friday, in a rental. Nor will I drive back on a Sunday. So if you're driving, I'd avoid those days. It can be frustrating for a visitor, especially in snow. A shuttle takes a lot more time, but somebody else is driving. And you don't need to deal with the car, parking, etc. in Aspen.
You need to shop hard for car rentals, if you do go that route. They are stupid expensive in the winter at standard rates. Renting in Denver is often worth it over the DIA prices. Seriously, the car rental piece is a challenge.
Last time we were in Denver we rented from Silvercar {Audi A4}. With a coupon, it was about $60 a day. Had a ski rack. We were not headed to Aspen, and needed a car.
Plan on a day getting there, and one getting back home. From either spot. Unless you are an iron man!
At any rate, flying out of NYC makes things a bit easier. Particularly to Whistler. We like arriving both at the destination and home not feeling exhausted.
Both great vacations. You'll love either one.