Chem 1A for the lab time since it is a 4 hour block and it can cause havoc if you phase 2 it and you don't get the time that fits your original schedule.
Definitely sign up for physics if you can, since there's no waitlist and it fills up like crazy. Chem 4B you'd probably be fine holding off until Phase II, which is what I did - if you're in CoC, they have to let you in anyway, and there are usually multiple time slots each day for labs. If L&S 160 is one of those easy discovery courses that fulfills a breadth requirement, it might fill up faster.
Just check the schedule the days leading up to your appointment to see which fills faster. And most math classes end up taking most of the people from the waitlist, since so many people drop in the first few weeks. If you can't get into a math discussion time that doesn't conflict with your schedule, just sign up for it anyway. You can try and switch later, or your GSI might be teaching another section at a different time that you could attend instead.
About UGBA10, I was thinking the same thing, but it gets mentioned in the DailyCal as having an average waitlist of 150, though with the new Tele-Bears system, this was reduced to 42. Still, that's a long enough list that you might not want to Phase 2 it. Just a thought.
