They are both terrible actresses. Rachel Taylor however from the first movie was pretty good in Bottle Shock.. even if she wasn't that great in Transformers..
Both aren't great actresses. However, almost every one of Isabel Lucas' lines seemed so ...forced and unnatural? I vote Megan. Her acting gradually got better as the film progressed.
Megan Fox... Although that's not saying too much. Isabel Lucas' lines were hilarious. Especially "My first car was my daddy's '92 Z28, fueeeeeel injected." Which is totally not hot, but hilariously funny, if you're a car guy.