Cruel Intentions is probably her best, I've seen the older adaptions (Dangerous Liaisons and Valmont) of the FRENCH (!) epistolary novel (Les Liaisons Dangereuses) and they really did a great job to turn the movie for a younger public.
I Know What You Did - quite good horror.
The Grudge I & II were also ok.
The Return was very bad.
Suburban Girl was not so special.
So my favourite is yes, Cruel Intentions.
SMG is gorgeous in Cruel Intentions. It baffles me why Ryan Philippe ends up with the other girl. If i'am honest i haven't seen a lot of her films which is annoying. I've noticed that especially recently her films haven't done too well, i hope that when she comes back to work she'll have a good film to work with.
Kathryn was gorgeous, yes, but she was also evil. SMG was really great in the movie. I haven't seen much film with her in it. I plan on watching Veronika Decides to Die soon.
I will always love "I Know What You Did Last Summer". That movie came out in the highs of the teen slasher flick phase and it brings back lots of good memories for me. 🙂