At first glance I would say Shuckle is the winner.
Blissey takes one physical hit and dies.
Blissey
HP 255
ATTACK 10
DEFENSE 10
SP. ATK 75
SP. DEF 135
SPEED 55
TOTAL 540
So you can see I truly horrendous Defense but a decent special attack and brilliant SDef. And of cousre that wickedly crazy HP.
Shuckle
HP 20
ATTACK 10
DEFENSE 230
SP. ATK 10
SP. DEF 230
SPEED 5
TOTAL 505
So we see the boss of all bosses in Defensive stats. But with an HP base stat of 20, he won't be taking much in terms of heavy hitters.
So overall Blissey turns out as winner. Even though she has an extremely low Defensive stat she has the HP and the Special Defense to stall pretty much any special attack you care to name.