The Marina tends to be younger, although I'm noticing a lot more strollers over the past few years than when I moved here 16 years ago. It still has a post-collegiate 20-something vibe to it, particularly around places like The Tipsy Pig, Campus, and Monaghan's. However, it's still possible to avoid this crowd if you know where to go. It's also close to the Presidio and Crissy Field, so if you're a walker/hiker/jogger/biker this is a real plus.
North Beach has the hills, the history - but this also brings in the tourists in droves. For a while, it seemed as if all new development and new businesses in the neighborhood had dried up - the old Pagoda Theater has been boarded up for almost 20 years. There have been some new recent additions like Park Tavern and Original Joe's which havebeen nice. The area around Broadway / Columbus had some problems for a while - a lot of wanna-be gang bangers were causing problems, which led to a large police presence in this area Friday and Saturday nights.
Hope this helps! Feel free to follow up with me if you have any more questions about these neighborhoods.
Better Homes & Gardens/Mason-McDuffie Real Estate
2200 Union Street
San Francisco, CA 94123
Marina- Flatter, foggier, cooler, generally younger renters, more flash, higher turnover, other than around the Marina Green it's less touristy.
North Beach- Hilly, more of a traditional SF neighborhood (buildings and people), more character, more touristy, more dense, less street parking.
Oggi Kashi - 415.690.3792 direct
Broker Associate, Paragon Real Estate Group CA DRE 01844627
All data from sources deemed reliable but subject to errors and omissions, and not warranted.