Whistler has consistent snowfall from Nov-mid April, but also gets rain to the peaks and dry spells during that time frame. I would say the interior has more reliable conditions snow wise, Whistler is just bigger. The problem is whenever it snows, half of Vancouver shows up. Even mid-week, you will line up on powder days (at least in the morning). If you do not time the opening of lifts right, getting untracked lines on the "best" terrain is hard, and you cannot spend 2-3 runs a lift figuring out where you go as it will be fully tracked in 60-90 minutes tops, also people will line up for the chair openings 1+ hour before hand so be mentally prepared for that (and agonizing over whether you made the right choice). Honestly, I love Whistler, but it's not a great place for a first visit as a hardcore skier unless you have someone to ski with to show you the ropes. You get better value/skiing in the interior (especially midweek when the resorts there are empty).
Also thee guy above is right, you NEED winter tires to drive these highways, it's not an option some days, so make sure your rental has them (yes, skilled drivers can handle them with all weathers but it's dangerous and stressful). 4WD doesn't matter on highway winter driving, winter tires do.