I have only been with DL 6 months. Spent the first 5 commuting from Den.
I've never commuted to anything but ATL, so I can't comment on the easier aircraft/schedules.
There are lots of flights a day between DL, UA, and SW. The bummer about commuting to the east is you lose 2 hours on top of the 3 hours of block time, due to the time zone change.
I usually reserved the Jumpseat, and commuted on us. I would say 75% of the time you'll be on a MD, and in that lovely Jumpseat no less - I can joke on it cause I fly it . Sometimes in the high traffic months, like ski season and part of summer, they'll put the ER on a couple of the flights.
Overall, I get the impression there are a lot of guys that do the DEN-ATL commute. If I didn't book the Jumpseat the minute it was available, I usually wouldn't get the one i wanted.
I would think the commute to SLC or MSP might be easier, but you'd have to check with those guys or check travel net. Lax could become an easier commute as the base grows.