Well, Speaking From My Over 2 years experience with the show, i would say she is, because she thinks things through, and tries not to mess up, and she sinabi in one episode " i have t hit the books at 7 each night" and she blew off hanging out with Ben and Kevin to "hit the books". also, she can remember spells and incantations on the fly, and knows how to react to situations in a smart and respectable manner.
I prefer yes and no both.Here are my reasons for yes. Yes: Gwen is known as the most smartest member in the group.She thinks before doing.She states things carefully and tries to understand before jumping to conclusions.She tries to think of logical explanations.Even in the episode where Mike Morningstar tried to drain her energy,she thought it through and then she took the "thing" which gave her,her powers back.She is definitely smart. No: She is just another character.And the main character is always smart.Plus,Ben has brainstorm as well.He is smart and can definitely kick any alien's butt any day.I would also prefer him.
I have reasons for both,so I have no choices presently.
Gwen is smart in one way but not smart in another way.
Gwen always thinks things through, But Ben always jumps to conclusions, and sometimes that works. So as you see Ben can sometimes be smarter then Gwen, but still she is really smart.And just to tell you Gwen is better at making up plans were as Ben is better at kicking alien butt, and Grandpa max well you will find out about Grandpa Max.
Gwen Has Brains and Power, but Ben has Has a army Grandpa Max has skills and Weapons.Kevin has a good side and a bad side. Tennysons and Levins are Smart and powerful people and Gwen,Ben and Kevin are one of them GO GWEN