Its an individual choice ..however on job prospective at both level you will be involve in R&D .
Here I will try to tell you few difference which would help you in choosing :
BioC is more intensive when it comes to studying detailed reactions of metabolic pathways (ie-knowing which enzymes catalyze each rxn, exact structures of reactants/products etc.) YOu will need to memorize tons of pathways in third yr, the structures of reactants/products, enzyme names, mechanism, etc. If you can memorize, you will do well and understanding the material in depth
MicB also involved a lot of molecular work, but probably at a more general level - not so much structures and pathways, but a lot of names of different cellular molecules that interact btwn host-pathogen for instance.micb may be a little more "applied science", as it involves a lot of the topics i mentioned earlier and how these are affected in the real world or how we can use microorganisms to our advantage. Microbio probably is more lab oriented !
Now make out what woudl you prefer ..what you would be able to handle !
Let know if I can help you further !
All the best !
both programs require a lot of the same core courses (basic cell bio, basic micro, genetics, orgo)...