By course do you mean a university course leading towards a full botany or microbiology degree? That's what I'd take it to mean in Australia. If that is the case, then if I were you, I'd steer clear of biology entirely unless you're willing to learn about evolution. Otherwise you'll be doing it wrong, and inevitably fail. Now that that's out of the way:
I did (and will keep doing next year) a double degree in biology and geology, and from the biology side I learnt to dislike botany quite a bit. Lots of memorization and pointless, obvious experiments - overall pretty dull, but there are people who love it. You might be one of those people. My experience with microbiology is more limited, but I found it to be more interesting and more relevant. Plus there's a broader scope for employment - you can go into medicine, lab work, health and safety, applied science (There's some very cool work being done with bacterial reduction of precious metals for example) - lotsa stuff.
If you're really keen on a biology education (and you're willing to learn about evolution) my advice would be to do a general biol course for a year and then specialize. This'll let you touch on all the major aspects (Botany, zoology, microbiology, ecology etc.) and decide exactly what it is you enjoy the most.
all that aside, IIRC you're still in high school, so if it's a high school class you're trying to decide on and easiness is all that matters, do botany. At high school level you'll do algae, mosses, lichens, ferns, gymnosperms and angiosperms, much of which is fairly straightforward (especially when they start reusing names, and you start to twig to the evolutionary pathways). This would be a lot easier than high school microbiology, where you'd cover all your different bacteria, archaea and micro-eukaryotes, plus you'd go into much more detail on stuff like fungi, algae etc. etc. - much more diverse and harder to study for come the final exam.
So yeah. High school, just want to pass, do botany. Want a career, do micro. IMO.
