If you can wait until the last minute, I would pick the mountains with the best forecasts on each day. Baker will likely have the most snow, so I would pick the day that looks like it will have the most fresh snow...this is all assuming you love riding powder.
Another thing to consider is that Alpental is not open on Mondays. So Monday is out if you mean Alpental when you say Snoqualmie. Also, if it snows a lot on Sunday night and all of Monday, Alpental can be amazing on Tuesday morning. It can be real crowded because everyone somehow finds a way to not be at work when there is a lot of snow on a Tuesday morning, but if you get lucky you could find youself with some really deep powder those days.