I answered drop bars but do also sometimes use my flat bar mountain bike. My bikes are ll either:

1. Drop bars with STI brifters (2 bikes)
2. Drop bars with down tube shifters (3 bikes)
3. Flat bars with thumb shifters (one bike)

I have sometimes considered drop bars on the mountain bike as well.

Edit: I should have mentioned that the flat MTB bars have a bit of rise, a bit of back sweep, and bar end extensions.