Okay from a pure stat point of view it's completely obvious who wins.
IF we go into movepool I really see nothing supporting Jolteon so obviously Thundurus-T would be better - his lower speed compared to Jolteon is made up by his base 145 SpA and overall, better bulk.
Thundurus-T @ Life Orb
Ability: Volt Absorb
EVs: 4 Def / 252 SpA / 252 Spe