I am a beginner that surfs in the SF area so I can definitely relate to you. I have been to Montara once when it was maybe 4-5 ft and it is a pretty heavy / steeper wave than anything you'll have seen at Linda Mar. With that being said the quality of the wave was definitely better. I surf Ocean Beach pretty frequently as well (when <6-7 ft) and the current at Montara is definitely not as strong as OB. One thing to watch out for is that when paddling out the the sand bottom drops from shallow to very deep quickly and the waves break pretty close to shore. With that being said, it's not a particularly far paddle out so when it's not huge there it's not too difficult. I am definitely going to try Montara again this summer. The time I went was a weekday before work, and I didn't experience any sort of localism, people were generally chill. Not sure about riding a longboard at Montara given how it's set up, I generally ride my 6'6 Firewire Addvance or 7' PU hybrid.
I feel that at Linda Mar it's almost always close outs and I find that there are only rideable waves once in a while when the swell isn't too large and there is some light offshore or mild onshore. With that being said I probably still go here the most because it's not crowded before work and I am not always fit enough to have productive sessions at OB. Riding something is still better than nothing. Agree with Princeton Jetty, it can get really good but when that happens you have all the local shredders taking over the one peak. When it's not so good it's hard to justify going there over Linda Mar unless it's less blown out.
Rockaway is a spot I have been starting to go more often as well as it is nearly empty during the work week and it has more consistent/longer rides, although the main peak is a right (I'm goofy). The paddle out is easy due to the channel and when it's around overhead and under it's not too scary. There is another peak in the middle that can be a good left or right but it breaks into rocks, which I have almost gotten thrown into before so I'm a little spooked until my endurance is better.
Sort of a long-winded response but just wanted to sum up my thoughts on the SF local breaks as I like you often find it too much commitment to spend a weekend day at Santa Cruz among the crowds when I can get to my local breaks in 20 min or less. I'd rather have convenience and less people at a less consistent break. I agree with RinkyDink that it may be worth frequenting OB to figure it out as it can be much better than Linda Mar (fall is great at OB). If I have to be honest I definitely spend 90% of my time at Linda Mar / OB. I still haven't figured out OB yet, but given the close out city that is Linda Mar, I think it's worth the time and building of paddle fitness (and yes, the paddle is truly rough).
Hope this helps. It's definitely tough learning in the SF area, but it's a good thing that when I need a break I am a frequent snowboarder and tahoe is less than 3 hours away, not to mention the great snow we've been getting
