well, weather doesn't matter, but I prefer blissey. It has a high spatk, which can help in rain, sun and hail. It also has blizzard, thunder and solarbeam for almost all weather usage. But, chansey can withstand a physical hit or psyshock holding evoilite, so it is your choice
Blissey (sun)@Leftovers.
252 hp, 52def, 100 spatk, 100spdef
Solarbeam (No charge in sun)
Flamethower (Boost in sun)
Toxic (Staller)
Protect (Staller)
Blissey (rain) @Leftovers
Same EVs as above
Thunder (Great in rain)
Toxic (Well...)
Protect (Well...)
Softboiled (Heals)
Blissey (Hail) @Leftovers
Same EVs as above
Blizzard (No miss in hail, great)
Sesimic toss (Special wall?)
Toxic (...)
Protect/Softboiled (Stalls, heals)
Blissey (Sandstorm) @Leftovers
Same EVs as above
Nature Gift (Hold Apicot berry)/mud bomb (Boost in sandstorm, accuracy lowering)
Sesimic toss (...)
Toxic (...)
Protect/ softboiled (...)
Typical stalling, but with attacking