Least favourite, I'd have to say Tali's. Haestrom on Insanity with the sun always frying your shields was not fun.

Favorite is probably Thane's, I just like the level design there. Ascending the towers is pretty cool.

Least favorite to do I would have to say Jack's, not because it's bad but because it's very hard on the eyes with the bright reds/oranges against a lot of darkness (I have sensory issues).

Fav: Tali

Least Fav: Samara or Jack