After 12 years, my answer has been finally locked in.
My favorite 'hero' class is definitely the grenadier, for a few reasons:
#1: Grenades are useless if not thrown by a grenadier.
#2: Grenades are extremely powerful, providing burst damage no other class can provide - if against a group of enemies.
#3: They usually end up with a good amount of shooting and burst skill, making soldiers obsolete.
(#4: They are the best drivers for PKs, if you are into those)
#5: Olli Heikkinen is a grenadier.