Tunnel-style may be best for left coast snow (I include n-Calif with the PNW due to its propensity for heavy, wet snow--both in the southern Cascades and northern Sierra). An example would be the Early Winters Omnipotent, which Bill Nicolai specifically designed to fend off the heavy Cascade snow. It was highly regarded by NW climbers. I went with the single-wall EW Winterlite as a lighter, less "bomber" option after having a really bad winter experience with an a-frame "mountain" tent with separate fly. To this day the Winterlite is probably my best winter tent.

Regardless of design, you will still have to get up and dig out periodically. Here's where an igloo or snow cave can be superior (if a heck of a lot more work). You just have to keep your airflow open.

Cheers,