Neither; Blizzard has a 70% accuracy without Hail, and unless you're making a Rain Team, Thunder isn't worth it without its weather. Even with wide lens, accuracy is only boosted by 10%. Starmie and Jolteon are both frail and will get KO'd if they miss. There are better moves for coverage, and considering the already high special attack of these two sweepers, the extra power isn't needed.
Starmie @ Life Orb
Ability: Natural Cure
EVs: 252 Sp. Atk, 252 Speed, 4 HP
Nature: Timid
- Psyshock
- Recover
- Surf
- Ice Beam
Ice Beam for coverage instead of Blizzard, and Life Orb instead of Wide Lens (since Starmie has no moves that miss). Also Timid nature over Modest; you need to outspeed Gengar. You have Jolteon on your team already, so no need for an electric move (it doesn't cover any of Starmie's weaknesses either).
Your team also has two Stealth Rock weaknesses, so Starmie could probably serve your team better by being a Rapid Spinner.
Starmie @ Leftovers
Ability: Natural Cure
EVs: 244 HP, 16 Sp. Atk, 252 Speed
Nature: Timid
- Psyshock/ Psychic
- Rapid Spin
- Recover
- Scald
Jolteon @ Choice Specs/ Scarf
Ability: Volt Absorb
EVs: 252 Sp. Atk, 252 Speed, 4 HP
Nature: Modest
- Thunderbolt
- Signal Beam
- HP Ice
- Shadow Ball/ Volt Switch
You might think that Scarf is not needed on a fast Pokemon like Jolteon, but I find it's basically a fail safe in case there's something like a scarfed Keldeo. Volt Switch to scout & escape.
I would Choice Jolteon rather than give it a Life Orb; I tried both Orb & Choice items on my Jolteon, and since it has no method of recovery, its longevity is limited by the HP recoil from Life Orb.
