From a tutor viewpoint, there are more people looking for H2
Physics tuition than H2 Bio tuition, so.... ;)
From what I heard from my students, H2 Bio is mostly
memorisation, pure mugging. For H2 Physics, I would say lots of
visualizations are needed; and the most basic test will be how well
do you really understand Newton's First and Second laws at O
levels. I have had students who got their As at O levels, but don't
really understand Newton's Laws.
Also, you mentioned you are passionate in studying Biology.
Passion is one of the most important consideration. If you don't
have the same or equally strong passion for Physics, in my opinion,
it will be better to take H2 Bio, because you will give your utmost
to do well in it.
My personal story in JC was that I scored badly for Economics,
but I really liked the subject. I put in extra efforts in it during
the later half of J2, and it never tires me because I really love
reading up about Economics. The first time I got a B was during
prelims, and the first time I got my A was A levels. Throughout JC,
I never scored higher than a C, but I scored at last. Passion
pulled me through. I was considering an Engineering-Econs double
degree after that, but NUS didn't offer it until my 3rd year. Until
now, I'm thinking if I would take a PhD in Economics in SMU in the
future (after my current Engineering PhD application goes
through).
I didn't think of Econs tuition at that time, or I didn't know
of any, or probably it wasn't popular back then. My classmates
helped me lots. But of course, I'm pretty sure the Econs tutor at
my centre will do a much better job than my classmates in
teaching 
