I usually prefer to fly on SQ 16 if i'm in Economy it is much less crowded than the 744. But more often than not i go via HK because I'm originally from there and is where a lot of my family is. If you've never been to HK, I personally think there is much, much more to see than Seoul(my personal opinon, so no one kill me). And on SQ2, because its so crowded the chances of getting upgraded are much higher if you are PPS. I got upgraded from Raffles to First coming back from SFO. But if you just want to get to SFO take SQ 16, especially because it connects well with your partner's BOM flight, 45 min is enough in my opinion, SQ is the #1 on-time airline in Asia Pac, so you shouldn't worry.