Jolteon

In the long run, the difference in dust and candies will be insignificant - the first one doesn't need double the candy/dust as the second to get it to level 30, which you'll reach before you know it. That said, Jolteons are good prestigers so it might be best to keep them where they are now (depending on their cp).

Depending on your opponent's moveset, and if you DO dodge, I prefer the thunderbolt one, if you don't, the thunder one.

Thunder is amazing and I prefer it on Jolteon, in fact for myself it's almost a must for both prestiging and attacking.

Thunder Bolt may suit your style better though, it's quicker and you can dodge more. If you prestige against a Twister-Gyarados you might get hit with two of those attacks while using Thunder. Now Twister may be nothing to a leveld up Jolteon but it takes its toll on a prestiging mon.

I am level 29 and have two maxed out Jolteons - one with Thunder and the other with Thunderbolt. Both are excellent for taking out Vaporeons and Gyarados. As Jolteons are not particularly robust, dodging will help them last a couple of fights. Since Thunderbolt allows for more dodging I prefer that one.

Just comes down to preference. Thunderbolt and Thunder do similar DPS per cycle. Thunder does slightly more (like 3% more in a perfect setting), but that assumes no energy waste, which will happen if you wait for the opponent to use their charge move before using your own.

Not saying you can't waste energy with Thunderbolt either, but there's more situations where you can use Thunderbolt safely over using Thunder without risking being hit by a full damage charge move.

Plus the one with Thunderbolt requires less candies to get to 30, which is a bonus. The difference in combat effectiveness between the two moves is close enough that it should come down to what is more enjoyable for you to use.

Level 33 and don't have a Jolt with thunder but have one at 2390 with bolt.
I honestly only use it for Gyrados as I have some high Venus's, a buttload of Exeggs, and I normally use Dragon for Vape. Oh and I'm building a Magneton for Lapras.
For your problem though, I'd recommend bolt, but the difference is negligible.
Bolt does a tiny bit less damage, but is a lot faster and far easier to dodge with, I would say against water pulse or aqua tail Vape you would want that ability to dodge over the small bit of increased damage, and certainly against speedy hydropump Gyrados it makes a difference.

How many Eevee's have you caught? They are very common in my area, but like you, I can count on 1 hand how many that are over 39+ in stats (I have found 3 so far out of nearly 300). At the end of the day, any high level Eevee is useful with either Vap or Jolteon.

That said, I agree with some of the posts that you simply need to play/level more and just evolve any ole high level Eevee you find. I have like 5 about to be evolved in the level 27+ range I think.

Like you also, I don't have a prime grass attacker or Dragonite or anything (free player here) and rely on 2 poor IV (0-48%) Jolteon's to do the job. They are both in the 1800 range and work perfectly fine honestly. I take down gyms daily and it could be a 2900 Vap, doesn't matter.

It's all how you want to play the game, but you wanted opinions and if you want to use your dust now on a 87% Jolt at level 26, have at it and enjoy the game you are playing. You may run into stardust problems later if you get a string of good hatches or catches.

That said, to your question, for lower level Jolteons, probably Thunderbolt, higher levels with slightly more hit points, Thunder...It is FAR more satisfying when you knock out over half the health of a Gyarados and it's dead...I prefer Thunder myself.

As for me, I wouldn't power either of these up...I eventually plan to power up a 98% Jolt w/ Thunderbolt, but that's after I have so much stardust, I can keep all my defenders maxed and have dust to spare (usually Lvl 34+ from what I hear...sitting on 750k+ after 3 powerups).

You don't even need to worry about IVs ... the posters are recommending that you catch a high-CP Eevee to evolve into Jolteon -- and then you've got something you can use to take down water and flying pokes (vape, lapras, gyarados, etc.).

If you're dead set on powering up one of the existing Jolteons, definitely go with Thunderbolt. It's slightly less DPS in a spamming scenario, but you need to dodge effectively to survive with Jolteon, even when you consider the type advantage over common gym defenders like Vaporeon. Thunderbolt is your best bet for effective dodging while maintaining legit DPS.

I've got one of each maxed out, and they're probably my favourite attackers. For fighting a defender with a single charge move I prefer Thunder, but against multiple bar charge moves bolt works better. I'd go with bolt first, but both are worth the dust investment for me.

Bolt is definitely better. When you fight high level water mons, you need 3 bolts, which means that you only dodge one hydropump or at most two aqua. However , if you have thunder, 1 hit is not enough but 2 are waste.