It depends on your team, your needs and your wants.
If you need a tank, go with Umbreon.
If you get yer kicks out of Psychic moggies owning anything that looks at it the wrong way, you want Espeon.
Want a Surfer? Go with Vaporeon?
Want to have a good old fashioned BBQ? Give Flareon a try.
Give yer foes an electrifying time with Jolteon.
Or show them that Ice Beam is a fun move to use with Glacia.
Or just beef up Leafia's Attack and go to town with Leaf Blade.
This sig for rent.
Up the airy mountains / Down the rushy Glen /
We dare not go a-hunting / For fear of Fairy-type Pokémon
The aswer to this question, of course, depends on which game we're talking about.
((WARNING: Spoilers! I know some people really, really don't like them, no matter how small.))
Keep in mind that your rival will recieve whichever "Eeveelution" that, save for if you chose Jolteon, can type-trump your choice (Rival will take Flareon if you chose Jolteon). Thus, I go with Jolteon.
This is a matter of taste. Considering that Dark types are fairly rare in GSC, I chose Umbreon, though Espeon is much, much easier to obtain.
Same guidelines as RBY, since you have to trade your Eeveelution over from FRLG, anyway. For Espeon and Umbreon, go beat Colloseum, and trade them over. You also get another Eevee in XD.
Espeon and Umbreon are available. In fact, they are your starters. Not much to say here, except that my Espeon always ended up with the higher level of the two by the time the ending credits rolled...
All Eeveelutions are available in this game. However, I chose Jolteon once again, as the three legendary birds and Lugia are put against you at the game's climax.
If you start as an Eevee, than a large leap had been taken in your journey to Eeveelution obtaination. If not, recruitment is required. Eevee can be found in the Joyous tower on floors 12F-17F. The three evolution stones aren't that much of a problem (they are found on the 29th floor of the Fiery Field, the Lightning Field, and the Northwind Field). To get Espeon and Umbreon, however, you need to bump their IQ up to four stars (or more, if you are so inclined), and evolve them using the Solar Ribbon (Espeon) or the Lunar Ribbion (Umbreon). Due to the high amount of "boss" psychic-types (Mew, Mewtwo, Deoxys...even Jirachi is part psychic-type), I chose Umbreon.
Though I do not yet own the game(s) (waiting for the english version. Even if those cheats are not longer available, I want to be able to transfer pokemon from my other games), and do not know of many of the specific in-game situations, I know that there are far fewer ice-types than grass-types in Shinou (Sinnoh?). Thus, Glacia (Which I'm pretty sure will be called "Glaceon" in the English release).
I hope this helps. I had to look through my old game guides to make sure the information was correct ^_^ I think it's fairly obvious, though, that I'm an Umbreon and Jolteon fan (mostly Umbreon, though). However, one major variable in Eeveelution-choosing is your own preference. Choose whichever Eeveelution you like best!
Depending on game, I tended to learn toward Jolteon (RBY, FRLG) and Espeon (GSC). That's in game, of course.
In the second case it's because Umbreon, as I recall, was hell to level up, whereas in the first, it's simple economics - I usually start Charmander so fire is covered, and good water types are much easier to obtain than their electric counterparts. (In GSC, the Flaffy line was readily available and decent enough in a fight, so Jolteon was no longer so useful).
"It is said that the federal government, if it was in charge of the Sahara, would run out of sand in five years. Private enterprise, being more efficient, would do it in half the time - and they'd make money off the bridges." - me.Originally Posted by Mintaka and Hurristat
"My friends, love is better than anger. Hope is better than fear. Optimism is better than despair. So let us be loving, hopeful and optimistic. And we’ll change the world." - Jack Layton's last letter. Rest in peace, Jack.
Vaporeon. Win both, and he gets a Jolteon. ...I think anyway. S'been a while.
That's interesting, and now I'm not honestly sure. I mean, every time I battled him (I remember being rather indecisive, and trying out all three), he seemed to have the one that was "strong" against mine...
But even besides that, Jolteon still helps with some of the tougher battles (Lance's Dragonite, as an example [STAB and double strength for its Flying qualities]). I'm gonna stick with Jolteon ^_^
Note that I'm not really a competitive or technical battler (I'm gonna try when DP cames out in english).
Sorry for any misconceptions or false information! I based a lot of this on my own inference (the guide check was just for the floor numbers in PMD, mostly), so i guess something had to be wrong :P