I'm from disted science stream and this is how feel:

Physics:
AS=very very awful subject teacher however the lab teacher was fine (there's a different lecturer for labs and theory)
A2=very very good teacher (very high praise for this dude )

Maths:
it depends on which teacher you get. there are 2 if i'm not mistaken. One of them (mr. chan is really good). don't know about the other one. also, you have to either take mechanics or statistics. i heard they got a new mech teacher so i don't know how he is. students generally really like the stats teacher.

Chemistry:
there are two different teachers and both suck

Bio:
i didn't take this subject but my friends who did say the teachers are great. one guy even said "the best lecturer at disted"

F. Maths:
it's generally a very very very very tough subject. be prepared to work your ass off if you're taking it and don't depend on the teacher too much.

If you're taking 11months (1 year), I wouldn't advise on taking 4 subjects. Regardless, even with 3 subjects, you might find that you're short on time to study, do past years etc..... but i feel that it's probably still be manageable.