Seattle to Whistler in January: What kind of rental car should I get?
 

What type of rental do I really need. 4 people with 2 bags and 3 snowboards. Place we are renting has parking for free. Assuming it's underground, what's the biggest car we can really fit.

I'd go with a midsize SUV. Underground lots can still usually fit anything except lifted trucks. The resorts are used to SUV's.

Agree with above. I have done this route many times most recently 2 weeks ago. For that number of people I would go for a mid to full size SUV primarily for the luggage.

The road up to Whistler is generally very good and stunningly beautiful.

All the underground lots have plenty of room for cars of this size.

The most annoying thing is having to pay for a rental and then having it sit unused for most of the time!

Just a heads up that road conditions sounded to be pretty slippery the last month between the Squamish to Whistler stretch with a number of bad accidents being reported on the evening news. Sounding like people driving too fast for the road conditions, particularly along some curves.

Have fun, stay safe.

If they offer a Subaru wagon - that is your ideal vehicle. Adequate trunk room and drives like a car.

A big fatal mistake is folks rent a bigger SUV and false impression on the road because they ride high and can't feel/see the road too well. Handling not ideal so they go faster and fault when lost of control or lose contact with the road. Unless the space is necessary - I strongly discourage folks rent SUV unless they are familiar driving them and understand the pros/cons (in bad weather conditions).
If you do decide to rent a SUV - go slower especially around turns vs. a car as it won't recover as well (unless you apply gas for traction = counter-intuitive) and won't stop nearly as quick as a car going downhill. If heavy winds you may want to follow the truck/bus ahead of you and just relax as speed won't win.