I'm surprised that people use Blissey and not Chansey.
Eviolite Chansey is better at everything (defensively) compared to Blissey.
Chansey reaches 178/463 defenses while Blissey reaches 130/369.
On the HP basis, Blissey has roughly the same as Chansey: Bliss 255>250 Chan
So only 5 in base, possibly more or less stat points than your eviolite chansey.^_^
If you ev train chansey like this: 252 def + 252 sp. def + 4 HP, you will DEFINITELY BEAT BLISSEY IN THE DEFENCES.
Chansey will probably always lack A BIT in HP unless: 252 HP + 252 def/sp. def + 4 speed.
Overall I think your best bet is eviolite chansey but technically it is your choice!
P.S: Blissey looks pretty fat... >_<
HOPE I HELPED ^_^