Zoology and Ecology were tied for the most interesting.
Microbiology is second.
Botany = Zzzzz
For me Botany was the hardest because it was the least interesting.
I would guess most people would rank microbiology and zoology higher than ecology and botany in terms of interest. But YMMV.
In terms of difficulty, micro tends to have pathways and techniques so there's a fair bit of memorizing but it tends to make sense. Zoology has a lot of systematics/evolution/life cycles/anatomy so there is a lot of "brute force" memorizing like memorizing clades, shared common characters, etc. Botany is the same way except with plants. Ecology is pretty easy because it has a lot of "common sense" applications. Eg if predator population goes up, what happens to prey population? it goes down.
In terms of the MCAT, microbio and zoology will probably help the most in bio sci. Ecology would only help a little. Botany wouldn't help at all.