Optimal Gyarados Defending Moveset vs Jolteon

All are good really. Outrage is pretty easy to dodge. Crunch and HP (rarely) but sometimes catch me sleeping depending on what I'm using. All 3 hurt a Jolteon since his HP is so low. A good Jolt wipes out almost all gyradoses I've come across before HP can happen.

DT/C is the best cuz it hits so frequently

All 3 with DT is very good otherwise if you want to be picky HP>Cr>Or. DT/HP is pretty much the old poliwrath with Bubble and hydropump

I have fought all of them. I find crunch the hardest to dodge, with outrage also being difficult. On top of that, if crunch is launched, you still can't really throw out your thunder safely, because it might be followed up by another crunch immediately. But maybe I just have to get used to these new moves. Also, if HP hits, it will usually kill your Jolt, which makes it the most difficult move to battle against if you are experiencing the gym bug.

I have a DT/Crunch Gyarados myself and fought him many times for prestiging etc.

All I can tell you is that it's very annoying to deal with him because he is almost all the time spaming crunch. I don't know about Outrage but definetly crunch is better than HP. Even with dodging DT/C Gyara could kill your Jolteon.

Crunch gets used frequently, due to lowest energy costs. It isn't a weak move (3x70). Hydro Pump can be difficult with the dodging bug. Outrage is extremely slow.

Outrage is very easy to dodge, the animation is too slow, you gotta be sleelping if you miss a dodge. Id say hydro pump and crunch are better defensive ms. And for me, the hardest of them to dodge is hydro pump, which comes out so fast that you may miss it.

If you have a decent Jolteon compared to the defending Gyarados, you can usually beat it before it fires HP, which takes HP out of the running. Between Crunch and Outrage, I think Crunch has the advantage due to being more difficult to dodge and being more likely to get hit while using a charge move, with its less predictable timing.

For similar reasons, a DT/C Gyarados is a pain to prestige up. The only time I've ever changed my mind about prestiging a gym with a Gyarados at the bottom was when I found out it had DT/C and concluded the benefit was not worth the resources (DT/C Gyrados at bottom, Blissey next, dodge bug present, ~9k prestige remains from lev 7 to lev 8). As I look on GymHunter just now, apparently nobody else prestiged it up either, and now it is lev 6 with Blissey at the bottom.

Crunch is better for defence for Gyrados because its not a tank so he may die before using hydropump.
Also 1 crunch prob kills jolteon anyways

I haven't fought a DT Crunch (or any crunch) gary yet... but I can say that I find an F-rated Bite Twister gary to be more challenging to defeat than a DT/HP one. I suspect DT crunch is more effective than DT/HP against jolteon (but not against anything that isn't a gary destroying electric)

Why? The charge move on the gyarados doesn't mean jack if it's dead before it gets to use it, which is often the case with a jolteon as attacker. Twister is always going to go off, and I find it extremely hard to dodge.
I live in fear of the day I face a DT-Crunch gary in battle with my insufficient stable of electric attackers; I'm sure it will mean that the attacker is only able to kill a single gary. And I only have a single jolteon attacker, and gary is about 20-40% of gym defense around here (lvl 10 towers with only 1-3 non-gary defenders are common).

HP is able to kill Jolteon in one hit, and it is hard to dodge.

Outrage is easy to dodge and mostly does less damage, but it come more frequently than HP.

Crunch comes slightly more frequently than Outrage, forcing the attacker to dodge often.

until they fix the feinting bug I'd say hydropump. After that couldn't say couldn't say and am curious about the answer to (after water event have everything except DT/OR which is what i was after) and am wondering which to power up if any (already have B/H and B/DP)

I fight Gyarados every day in my area, and I would say DT/HP is toughest.

Of all the "big" moves in the game, HP is the hardest to dodge, and can knock out a Jolt in one hit. Crunch is annoying, sure, but isn't a knockout punch.

Plus, HP is far superior on attack, for when he's not in a gym.