I fly out of SFO too. I wouldn't say there is one best answer. Having a subscription to EF helps as you can check upgrade inventory and seat availability. I'm usually booking 1-3 weeks in advance, so I'll typically check routes on my travel day for upgrade inventory. Then I'll look at FC seat availability on the day of the week I'd be traveling, but on the soonest upcoming date.

I tend to avoid SLC since you'll almost always have a CRJ-700/900, and it offers the least MQM's. Upgrades tend to be decent on this route though, so if you don't care about a smaller plane and less MQM's it is a good option. If I am going to have a 1+ hr layover then I prefer ATL or MSP to spend time in (MSP being my favorite).

Sometimes you can get lightning delays at the hubs, but I find that DL hubs have MUCH fewer WX delays compared to UA/AA. I'm almost always on the last flight home from the east coast or midwest, and have only had to overnight due to WX one time in the past 2 years.

Getting on the MD-88/90 is a good choice for upgrades, and if you miss the UG you can get the side with only 2 seats in EC usually. Going through ATL can be tough, but they usually run a 757 with 6-7 rows of FC. I avoid CVG.