Lucky punch blissey should never be used, but evoilite works amazingly well.
Blissey, to me, has a few more roles than chansey.
I like to use a counter blissey with a focus sash to insta-kill any physical sweeper especially boosted stat ones.
Also, if you're UU, you can't use chansey, so blissey is the other option.
The bulkier is chansey, but it depends on your teams weaknesses, like if talonflame is a threat blissey would be perfect.
Blissey@ focus sash
-counter
-healing wish
-stealth rock
-anything else
Chansey@ evoilite
Ability: healer
Evs: 252 HP; 252 Def; 4 Sp def
Nature: Def +; atk -
-toxic
-stealth rock/ wish/ soft-boiled/ heal bell
-counter/seismic toss
-stealth rock/ wish/ soft-boiled/ heal bell