Eeveelution

Flareon is great budget attacker.
Jolteon also do well, when need electric dmg( mainly in gyms) and you wont invest in Legendaries.
Vaporeon is slighty behind them, but is still okay attacker and bulky, annoying defender with Aqua Tail.
Espeon is top choice against Machamp raid, but i dont see other use for him.
Umbreon is the worse among them- really bad on offense, and quite poor in defense with his mono dark moves.

In future evolutions, Glaceon and Sylveon will be great mons. Glaceon have chance to be top Ice, if Mamowine wont have Avalanche while he will have it.
Sylveon with double fairy will do very well.

Leafon probably could earn similiar status as Vaporeon in offensive- Sceptile, Frenzy Plant Venusaur are better. Tangrowth probably also will be better.

I like all the Eevee evolutions as budget attackers/defenders. They aren’t the greatest now at what they do, or will do, but a great second or third choice. Espeon and in the future Sylveon are great for dropping in gyms in between Blissey and Snorlax, so you have to change from Machamp.

I think Umbreon and Vaporeon are the least used because of Gyarados and Ttar. Both are fairly common and far ahead.

Like said by the others, they're all great budget attackers (with the exception of Umbreon).

Vaporeon: Outclassed badly by Gyarados.
Jolteon: Currently best non-legendary electric type.
Flareon: Currently best non-legacy non-legendary fire type.
Espeon: Tied for best non-legendary psychic type in all generations.
Umbreon: Unfortunately obsoleted by its defensive stats. Clearly the least useful one.

Glaceon: Almost guaranteed to get a good moveset, which will put it in top 3 of ice types.
Leafeon: Dependent on movesets, will be a decent to good grass type.
Sylveon: Guaranteed to get double fairy moveset, unlikely to make big meta waves even with that, but gen 6 is a long way off.

The most future proof of them is by far Espeon, who holds the mantle of having the second highest attack stat of non-legendary psychic mons *in all generations*. All the others get outranked by other non-legendaries at some point or another.