I know it got rejected earlier, but I'd like to have it reevaluated. It has a really great Speed tier where it is barely out sped by anything that isn't scarfed. It's resists Bullet Punch, as well as Talonflame's Brave Bird, and Mega Pinsir's Quick Attack. Because of Jolteon's Speed, it can OHKO a lot of common threats. The only problem I find is that it's forced to run Choice Specs to deal a a significant amount of damage for OHKO's on many common threats, and it can really only come out for revenge kills.
Calcs:
+2 252+ Atk Aerilate Mega Pinsir Quick Attack vs. 4 HP / 0 Def Jolteon: 161-189 (59.1 - 69.4%) -- guaranteed 2HKO
252+ Atk Choice Band Talonflame Brave Bird vs. 4 HP / 0 Def Jolteon: 177-209 (65 - 76.8%) -- guaranteed 2HKO
+2 252+ Atk Technician Mega Scizor Bullet Punch vs. 4 HP / 0 Def Jolteon: 181-213 (66.5 - 78.3%) -- guaranteed 2HKO
252+ Atk Choice Band Huge Power Azumarill Aqua Jet vs. 4 HP / 0 Def Jolteon: 180-213 (66.1 - 78.3%) -- guaranteed 2HKO
252 SpA Choice Specs Jolteon Thunderbolt vs. 4 HP / 0 SpD Talonflame: 530-626 (177.8 - 210%) -- guaranteed OHKO
252 SpA Choice Specs Jolteon Thunderbolt vs. 4 HP / 0 SpD Mega Charizard Y: 348-410 (116.7 - 137.5%) -- guaranteed OHKO
252 SpA Choice Specs Jolteon Thunderbolt vs. 4 HP / 0 SpD Mega Pinsir: 428-506 (157.3 - 186%) -- guaranteed OHKO
252 SpA Choice Specs Jolteon Thunderbolt vs. 252 HP / 4 SpD Azumarill: 470-554 (116.3 - 137.1%) -- guaranteed OHKO
252 SpA Choice Specs Jolteon Hidden Power Ice vs. 4 HP / 0 SpD Dragonite: 352-416 (108.6 - 128.3%) -- guaranteed OHKO after Stealth Rocks
Notable fast Pokemon it out speeds:
Talonflame, Greninja, Mega Pinsir, Gengar, Infernape, Garchomp, Keldeo, Dragonite at +1
Thanks to Volt Absorb it can come out of Electric-type moves such as Volt Switch, and gain some lost health.
Of course it can out speed many other threats, and possibly OHKO them, but I just wanted to list Pokemon that are relevent that Jolteon can take down.
I'm not sure if it's outclassed by anything, but I just wanted to throw this out there.