Which is faster? - modifying css property or adding class in jquery

Question

I have about 100 elements in like and am trying to create an animation with jquery.

I need to a

Answer 1

which of them is rendered faster in browser:

Depends on the browser. you should do some tests if it's interesting you.

Anyway it's not important and very unlikely to be the bottle-neck of your website.
Avoid micro-optimization, "premature optimization is the root of all evil", you're wasting your time.