Vaporeon: AT vs HP?

yup

Nope, you might get WP.

If you like to dodge, Aqua Tail. If you like using charge moves as often as possible, Aqua Tail. If you don't dodge, or is lazy -- Hydropump!

Personally, I like Aqua Tail. I like to dodge. I wish my squad of Vaporeons were mainly Aqua Tail. Sadly, they're mostly Hydropump. I'm fine with them having Hydropump, but its just that I really prefer Aqua Tail (dodging).

No, you have 50% chance to get water pulse, witch is terrible. AT is a great move and many players prefer it over HP.

Aqua Tail is fine. Great actually. Hydro Pump does outperform it in pure DPS, but Aqua Tail does have it's advantages: it's low cooldown allows for reliable dodging, it's low energy means you get consistent damage output - if you faint with an almost complete energy bar with Hydro Pump then you've lost out on a significant amount of damage. The difference in damage between 2 or 3 Hydro Pump cycles is much bigger than the difference between 5 or 6 Aqua Tail cycles.

It also means you get less energy wastage from taking damage - sometimes your charge bar is almost full but you get hit by a charge move, but that extra damage is not converted into extra energy past 100, where it would be with Aqua Tail because you'd always have low enough energy from using your charge move as soon as it's available.

e.g. if you're at 90 energy and you take 50 damage, you'd usually gain 25 energy, but since you can only have a maximum of 100 energy, 15 energy is wasted.

In the case of Hydro Pump that has 130 base damage for 100 energy, 15 energy is roughly equivalent to a 20 base damage move.

I'd stick with it unless it is maxed out already and you have TMs to burn.

Water Pulse is the risk here, but at least WP has the coolest animation, in my opinion.

I prefer AT myself.
With a 50% chance of WP it is suicide.

I plan on using spare TMs later on WP Vapes and won't care if I get AT or HP

After reading the comments here, I powered up my highest IV Vaporeon from 23.5 to 28.5. He is 96% IV (14/15/14) with WG/AT.
I don't have any higher level AT Vapes either, only HP ones.