If you want a fast special attacker, I'm going to say Espeon. Magic Bounce is an absolutely phenomenal Ability, and Espeon is a brilliant special attacker. It's fairly frail, so Rash's Special Defense drop won't matter too much.
Espeon @ Life Orb / Choice item
Ability: Magic Bounce
- Psychic / Psyshock
- Shadow Ball
- Dazzling Gleam
- Calm Mind / Trick
If you want a tankier special attacker, Sylveon is probably the best. It has an excellent 130 base Special Defense, and Pixilate allows it to hit pretty hard as well.
Sylveon @ Leftovers
Ability: Pixilate
- Wish
- Protect
- Hyper Voice
- Mystical Fire
Glaceon and Jolteon are both pretty solid as well, so use one of those if you so choose. Glaceon has a very shallow movepool, and Jolteon is quite frail, so be warned. Glaceon's Ability also doesn't really benefit it without extra support, and Jolteon is usually better without HA.
Glaceon @ Choice Specs
Ability: Ice Body
- Ice Beam / Blizzard
- Shadow Ball
- Hyper Voice
- Freeze-Dry / Icy Wind
Jolteon @ Choice Specs
Ability: Quick Feet
- Thunderbolt / Thunder / Discharge
- Shadow Ball
- Volt Switch
- Hyper Voice
Hope I helped!