Seeing that next year's SMOFCon will be in Santa Rosa, I visited its website from curiosity. I'm unlikely to go - even when I was working on conventions, they were of a different order or my work was of a different kind and I wasn't part of that community - but I was curious as to their site - is it in an area that was affected by the recent fires? No - and the directions.
On that, I have a few comments.
They recommend San Francisco (SFO) for flights, and do so on the grounds of its larger size and greater number of options. I wouldn't put it that way. I'd say that those are the reasons you might find yourself using SFO regardless of whether it's the best airport or not.
When I'm picking among multiple possible airports, I start by figuring out which one best fits my ground transportation needs. Then I see what the flight options and costs are. Only if some other airport's advantages in that respect outweigh its ground disadvantages do I switch.
So if you just want to go to Santa Rosa and not drive around a lot, Sonoma County (STS) is obviously best. The site says fares there can be quite high. I'm sure that's true (I've never had to price them myself), and that could indeed drive you to consider SFO or Oakland (OAK) even if you had no plans to visit those cities.
But which of SFS or OAK is logistically superior, leaving aside which has more flight options? (And OAK has some non-stops to unexpected far-off places: it could surprise you.) You have to weigh those.
SFO is far more likely to be socked in by fog, and that's a consideration at this time of year.
OAK being smaller is frequently less crowded. However, my minimal experience there says that security checkpoints are more likely to be overwhelmed there, and once I saw baggage claim chaos at OAK worse than almost anywhere else.
The site says SFO has an airport shuttle; it doesn't say about OAK, but actually the same service goes to both.
Both are major airports as far as airline and rental car selection are concerned.
If you drive, the difference in traffic is likely to be a wash. SFO directly connects to the 101 freeway, but you have to drive on surface streets through the City. OAK is a long mile from the 880 freeway, but once you're there it's all freeway. Commuter traffic, if you hit it, can be very bad on either, but it's worse on the OAK route, at least in the part of the route that's I-80, between Emeryville and Richmond.
Bridges. You have to cross over one on each route, and they both charge tolls, but in one direction only. SFO-Santa Rosa goes over the Golden Gate Bridge, which charges toll on the way back. Those tolls are only taken electronically, so you'd best talk to your rental car company about that. OAK-Santa Rosa goes over the Richmond-San Rafael Bridge, which charges toll on the way to the con instead (I could explain the discrepancy, but you wouldn't want to read it), and that one does still take cash, $5 for cars.
However, if you've never been over the Golden Gate Bridge, then for Ghu's sake do. It's one of California's finest sights. But that gets into tourist attractions, and that's another post. This one is just practical logistics.
There's another airport option, you know. Sacramento (SMF). Check flights to that. There's no toll bridges on the drive. While SFO and OAK are 70 miles away from Santa Rosa, SMF is 100 miles, which is not that much of a difference at that scale, and for most of the route the traffic will be less, unless you hit holidays. Google Maps will route you through Vallejo, which looks at first glance out of the way. If efficiency is the goal, I'd go down I-80 at least as far as Hwy 12 at Fairfield. The direct route over Hwy 128 and local roads is scenic, so it's good for meandering, but it's mountainous and twisty and will save you neither miles nor time if those are concerns.