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Jolteon and espeon are both the best thanks to how few of their type is in the game, and how few pokemon there are that break 100 speed. Jolteon is better thanks to t wave making it easier to catch shadow pokemon
Umbreon is a solid choice, but thanks to how many dark types there are in the game, especially early on, it isnt as strong of a choice (though most are offensive unlike umbreon who is defensive)
Vaporeon is also a good choice, though its usefullnesss is downplayed thanks to its best STAB option being water pulse (60 bp) for most of the game. Youll evetually get hydro pump later on, but thats post game (mt battle), and when you beat the game, you can just trade it over to teach it surf
Most of what flareon, houndoom can do better. Still, give it overheat, and if your houndoom has flash fire too, the two can work reasonably well as a pair (shame overheat doesnt affect all on fieldd pokemon)