I live in Seattle and ski both Crystal and Snoqualmie Summit often. Assuming you're hardboot carving (as opposed to skiing), and based on your Buttermilk green/blue comment here's my recommendation: Go to Summit West (one of the four Summit-at-Snoqualmie options) on Wednesday afternoon -- West is closed Monday and Tuesday and they open at 2pm on Wednesday after a thorough grooming overnight Tuesday (I assume; they might groom on Monday for all I know.) The pitch is a consistent green-blue, and while there's not quite 700 feet of vertical, the one chairlift accesses a half-mile-wide field just ready for trench time.
You'll drive up in an hour, you'll carve your legs into oblivion in 2-3 hours, and the Timberwolf bar is one of the nicest places for an after-sesh beer or cocktail. Sixty more minutes down I-90 and you can be home for dinner. This works any weekday with no lift lines, but Wednesdays are best IMHO.
If you can only carve on weekends, Summit West is good for carving but get there early as they open at 9am, and the parking lots will fill up with ski school families and general mayhem.
Crystal might be a better bet on weekends; a bit crowded, but the high speed lifts help. Forest Queen chair is the ticket for great grooming and high-speed six person uphill returns. Crystal has higher elevation, which can mean snow at Crystal when there's rain at Snoqualmie.
For me, the short drive to Snoqualmie combined with mid-week lack of crowds tips the scales. But check the weather, and hit me up for a carve session!