This is not a matter of fact but of opinion.
I find it rather elitist to presume who's the best. To make such a judgement, one must first put themselves into a position of superiority. As I believe all human beings to be equal, I would never put myself into a position where I would claim to know what is or isn't best.
However in my opinion I find Gromit to be the most expressive character in that he seems to be a reflection of Nick Park's state of mind.
IM A SUPER FAN OF WALLACE AND GROMIT AND FOR ME THEY ARE ALL SUPER SUPER GOOD,IF YOU DONT FIND GROMIT COOL OK,THATS YOUR OPINION BUT NOT EVERYBODY HAVES THE SAME OPINION LIKE YOU!!!!
AND PS: RUUUUUUUUUUUUULES,JEJEJEJEJEJE
DONT TAKE THIS PERSONAL BRONNY,BUT DONT BRAKE YOUR BRAINS OUT BECAUSE PEOPLE LIKES SO MUCH