Here is my take, and take into account I am wickedly biased and love Stevens Pass.
Alpental bc is great. No question about it. My problem is on 3 fronts: it is well known to have good backcountry, so more people frequent it; it is really only confined north of the area, so all those who venture into it venture into a relatively small area (it is still big, but relatively speaking); and you can only access it via one lift..
Stevens backcountry is really more confined to smaller, but more numerous areas. One disadvantage is that much of it (but certainly not all of it) is tamer than that of Alpental, and sections that are considerably steeper/XTREEEEEME are shorter and harder to come by. But, since BC access is available on the northside of the highway, off of double D/southern cross, tye/jupiter, and 7th and sky, you have quite a pissload of options. Plus if you drop to the highway its about 3.000ft vert, so it is far from insignificant.
Of course, this leads to the potential for more hiking to and from, depending where you go, as well as very diverse conditions.
Anyway, it is good stuff, but it is getting hit more and more. You aren't really sacrificing anything.