SFO-SEA is usually mainline save for one or two flights a day. SFO-PDX is also mostly mainline. (Equipment on both routes can fluctuate based on day and season.) At least UA's (well, Skywest's) CRJ-700s have Economy Plus and First. Having said that, I'd definitely take VX Main Cabin over CRJ Economy Plus, and possibly even over First, all things being equal.

But as lainys pointed out, things aren't all equal when UA 1Ks can often rely on free upgrades (or pre-boarding, Economy Plus, and drink chits for when upgrades don't clear). OTOH, as we know, sustained loyalty to VX would yield no perks whatsoever. I'm afraid I'll be keeping the lion's share of my business with UA (mostly mainline) until VX evolves its upgrade program beyond just increasing the price of cash upgrades every few months.