The lie flat seats were great, it was my first first class experience,
but unlike other airlines there were window seats and aisle seats. So
I had to climb over the guy sitting next to me in order to get up
during the flight.
That must have been an older aircraft, their new business seats all have direct aisle access.
I’d be flying from San Francisco to Copenhagen to Paris R/T. It would
be economy or econmy plus. Can’t afford 1st class which I’m sure was
nice. Badger, I’m wondering about seat comfort, legroom, headroom,
cleanliness, flight attendants nice, good entertainment system for the
transatlantic leg.
The aircraft are clean. I've never flown on an SAS aircraft that wasn't clean, although I have seen some older ones that have felt a bit worn but still well maintained. They are however in the process of upgrading their entire fleet so the risk of ending up in an older aircraft is not that big. The flight attendants have always been nice but they are Scandinavian so they will not stop by you every 5 minutes to see if everything is fine. (Side note: I have seen people, often Americans, complaining about bad service in Northern Europe. It is not bad, but there is a cultural difference. It is about respecting the customers privacy and not interrupting them more than needed. But if you need anything, just ask.)
For the transatlantic part SAS used to fly A340s to San Fransisco, but they have now sold the A340s and replaced them with A350s. But with the pandemic the route planning has been upset a bit and you might end up on an A330. The economy seats are good enough. I've so far never encountered an airline where the economy seats are can be called comfortable but the SAS seats are on the better end of the scale. The premium economy seats are better though being a bit wider and with a bit more legroom. And Scandinavians are tall, so no need to worry about headroom :-)
Transfer in Copenhagen is fast and easy. It is a much smaller airport than the megahubs so usually the arrival and departure gates are only a five minute walk or so from each other. But still it is big enough to have a decent selection of bars, restaurants and shops if that is what you are looking for. And if flying premium economy you'll have access to their lounge. Copenhagen also can separate non-Schengen arrivals from "safe" and "unsafe" countries so no need for extra security on the way to Paris, just an immigration check.
For the intraeuropean part, SAS uses A320s on the flights out of Copenhagen (they have 737s as well, but those are based in Oslo). Most of them are A320neo that are noticeably quieter than older aircraft. Like most European airlines, the seats are the same in the entire cabin and the difference between economy and premium economy in the service. But legroom is a bit better than Norwegian and other low cost airlines. Food is served to passengers in premium economy, those in economy get coffee or tea for free and can buy other food if they want. SAS do not block the middle seat in premium economy, but in my opinion they try to keep it free. So there is a pretty good chance you will get an empty seat next to you in premium economy, but no guarantee.
In my personal opinion you should book Plus (premium economy) if you feel the price is acceptable. That will give you access to fast track security & lounge access (where available) and free wifi during the flight (available on most aircraft).