Firewall the best. There's a very tight storyline in Firewall, due to a deadline that is quickly approaching. I think the author did a great job in sticking to and following the dates and times in the book, sort of like a season of 24 but instead of one day it lasted less than a week. I feel so sorry for Taryn, the story starts as she's about to go on her honeymoon but there's an airport bombing and her brand new husband is gone! She barely survives and now has to deal with who and what her husband might be.
Moment of nitpickiness: the cover picture doesn't match Taryn's description - she has red hair and green eyes. :)