Wat do I do
Just found this monster on a walk tonight (just got home actually)
Should I evolve it now and hope for non-Flareon? Or get a guaranteed Espeon?
I'm leaning towards Eeveelutions since Alakazam and Mewtwo can substitute Espeon. I REALLY don't want a Flareon though. Jolteon would actually be preferred for Blizzard Kyogre but that's only a one-in-three chance.

Answers
Weather boosted Eevees aren't too uncommon. I'll certainly save a perfect Eevee for that (as I've hatched one and caught two others since I find them often here), but I don't want to save this one for a year when the need (and potential benefits, such as additional Premier balls and saved potions) is present.
Just wondering, why do you not want Flareon? I would actually say Flareon is now the best Eevee-lution, with Kyogre crushing Vaporeon.
After Gen 2, Vaporeon wasn't the best Eeveelution because of its stats and moves, but because of lack of competition. Now, all the Eeveelutions have been outclassed by legendaries. But Flareon performs the *closest* to the legendaries, with the same DPS but less bulk.
Edit: Considering the current state of EX raids, Espeon can be said to be on par with Flareon as an Eeveelution.
Flareon would certainly seem like a good option, being that the weather in my area is often Clear.
However, it doesn't offer much meaningful coverage. It is pretty good for damage, but I have already invested the candies to max a Moltres and have enough candies to take an Entei to level 32. I already have a few Flareon and Arcanine in the 2.4-2.5k range, and I also just evolved a Blaziken at nearly 2.4k CP with Overheat.
The coverage that Fire-types offer would be against Celebi (Which should be covered by my Scizor, Mewtwo [SB], maxed TTars, and potentially Rayquaza), Regice (Covered by Machamp), and Registeel (Covered by Machamp and Groudon).
If you really want to look ahead, the Swords of Justice can all be countered by alternatives such as Machamp, Groudon, and Mewtwo/Espeon/Alakazam/Gardevoir.
Note that I am set to have a maxed Moltres and partially-powered Entei in addition to having a few level 30 fire-types already. Though I live somewhere with Clear weather, this also means that I can find high-level Fire Pokemon wild. Good electric-type can't really be found wild, and rain is very rare here (and I am unlikely to find a very good weather-boosted Feebas, Magikarp, or Mudkip). I also simply won't have the resources to power an army of Kyogres, and I would much prefer one or two maxed Kyogres to 6 partially-powered ones.
Electric-types are very important right now with the advent of Blizzard Kyogre, and I don't have more than one Raikou and Zapdos even partially powered up (theyre currently sitting at a mere level 30).
Water-type Pokemon will always be relevant, though, with the exception of Gyarados, they are eclipsed by a far greater margin than the rest of the Eeveelutions are (Whereas Flareon actually boasts higher Attack and Defense than poor Entei).