"I love the way she dressed today" -past simple (this implies a completed past time, so she dressed well on this particular occasion but maybe she doesn't always dress so well)
"I love the way she dresses today" - present simple (this would be used if you like the way she dresses in general/ all of the time). I agree with Madelyn, I wouldn't use 'today' in this sentence. You just could say: I love the way she dresses.
which sentence should I use?