Fighters are sticky in a second way, via combat superiority. No other defender has a second Sticky class feature. Hence, my belief that being "Sticky" is what defines a defender, and fighters are more "Sticky" than the other defender's we've seen.
If all attackers are melee based, then I can see this argument holding sway over most of the others. However, IME (and almost always IMC) there is a variety of attackers ranged and melee.
So here is my view on Fighter, Paladin and (defensive) Swordmage.
Vs. Melee
Fighter
- If opponent shifts away, it suffers Immediate Interupt attack and must either Charge (at -2) or use it's Standard action to move into position.
- If the opponent moves away, it suffers OA that stops the movement on a hit.
- If the opponent attacks another target in range, it suffers a -2 attack penalty and an Immediate Interupt attack.
Paladin
- If the opponent attacks another target, it suffers a -2 attack penalty and 3+Cha Holy damage.
Swordmage
- If the opponent attacks another target, it suffers a -2 attack penalty and any damage dealt is reduced by X (don't remember the formula).
Vs. Ranged
Fighter (if starting in melee range)
- If opponent shifts away, it suffers Immediate Interupt attack and then may attack as normal at a -2 penalty.
Paladin
- If the opponent attacks another target, it suffers a -2 attack penalty and 3+Cha Holy damage.
Swordmage
- If the opponent attacks another target, it suffers a -2 attack penalty and any damage dealt is reduced by X.
So...
Fighters are better at stopping melee opponents from getting around them, but don't do much of anything against ranged opponents (especially those who stay at range).
Paladins don't (by mark alone) stop opponents from attacking their allies, but punish them for doing so regardless of battlefield position.
Swordmages reduce/negate damage done to any allies.
Three different styles of having the same goal -
protect allies by making enemies attack the defender. Each are quite effective when used properly.