What's your favorite method for making animations for your game and why?
Do you draw the sprites in a traditional way? Or do you make them in a way similar as Brawlhalla does?
Do you use procedural or traditional animation, and why?
UpsetChicken Best way is to combine both in a complementary fashion. Use the more suitable one for each specific animation problem.
My favorite is 3d. If I have to do 2d, I make an animation in 3d, cartoon shade it, and export it frame by frame. You can still tell it's 3d, but so many people do it now, it's ok.
Well this is 3D exported frame by frame :
Since I can't draw at all 
I prefer traditional in most cases because it's easier to make it look good, but I don't hate procedural. it's just that so much of the computer generation is too smooth, it doesn't look natural unless you really fiddle with it and add touchups of your own.
turning 3D models into 2D sprites can look very natural with enough elbow grease. I didn't even know that's what Dead Cells does until I was looking for examples for this post!
and let's not forget digitization, where you take a picture of a real object and make it into a game sprite. Doom was very fond of that, the weapons are all pictures of real toys you can find and the monsters were pictures of clay models. very easy to animate when it's "move your arm a bit and take another photo"