There have always been comparisons between Alias and Buffy... because they both have female main characters who kick butt.
I liked Anya. She was kind of annoying, but Emma Caulfield played her well... and I love the whole thing she had against bunnies.
Lauren on the other hand... I don't think even a little bit that she's the best thing to happen to Alias. Actually, she might be the worst. The character of Lauren is not someone that makes me want to watch the show. In fact, it makes me want to grate my teeth at the bad-ness of the character and turn the tv off.
I think Melissa George is a perfectly fine person, but she isn't playing Lauren very well... but that might just be because the character isn't written well at all. Lauren is one of JJ Abram's weakest character creations (and I watched all 4 years of Felicity as well). I'm very glad that MG is not going to be a regular next season... not because I dislike her, but because it means Lauren will take a backseat.