I've done TPE-SFO and back in Y quite a few times in the last year or so on BR and it's almost always the 777 with the 3-4-3 layout. Sitting in a window I don't think I've ever had an empty seat next to me.
The 3-4-3 seating is tight but doable, obviously the 3-3-3 has a bit more space. There are some seats with the box in front but it's not huge like on the A330s, still enough room to stretch your legs but you might not be able to do so if you have a packpack under the seat too. I seem to remember that at least on the sides, not every seat has a 'leg' at the back so you might get a bit of extra room if your neighbor doesn't have their bag under the seat in front. Right up the back it goes to 2-4-2 for the last few rows but I've never been able to snag one of those when checking in online 48 hours out.