My least favorite is creepers..need I say why? You don't hear them...until it's too late. Aweful when they explode near your contraption and make everything break..creates messes...I hate them.
My favorite one would be..baby zombies.
It's funny because my most hated mob is the baby zombie haha, and my second favourite is the creeper!
They have tiny hitboxes, they're lightning fast, they don't burn in daylight, yet they do as much damage as grown up zombies... run into one with an enchanted sword early in the game and you'd be lucky if you escape with your life xd.
My second favourite mob is the creeper, just because explosions are awesome. Though they can be quite annoying and damaging towards your hard work so yeah...
Pyromniac as I am, I would have to say that my favourite would be the blaze. They look menacing, and their attacks are quite fun. They're my favourite, although I do try to avoid them until I get fire resistance potions...
Most hated: Either Baby Zombies or Skeletons.
I absolutely hate the baby zombies. Every time I see one, it's always too late. I take 2 or 3 hits, and then see them sprinting at me. Scares me every single time.
Otherwise, Skeletons are the most annoying. Maybe it's just me, but I swear the skeletons in my world have almost 100% accuracy.
Seriously, they're pretty useful for getting around. Only exceptions are when you're trying to get through a forest, and when they wander off when you dismount, often back to where you just left from.