I think in general, the sequels ruined these characters, because I actually didn't mind Evan in the first Monster Blood, and I didn't mind Greg in the first Say Cheese and Die. I, however, loathe Gabe in the first Mummy book, and that's why he gets my vote for worst protagonist.
He's whiney, he's insecure, he has a masculinity complex, he is boastful... The scene where he happened to know how long the base of the pyramid was and Sari didn't, where he stuck his tongue out at Sari as a way to boast about answering the question correctly... He's the kid we all hated in school.