I like to take I-90 eastbound and westbound because Highway 2 is steeper and I finished off a set of brakes once coming down off Stevens Pass going to Seattle. Highway 2 is the more scenic drive though in my opinion.

Even if you take 90 and then 97 (Blewett Pass), you can still hit Leavenworth, it's not that far from where 97 intersects with 2.