I'd go with Espeon for higher special attack and psychic type coverage. For your last team member, I'd recommend Gengar or Nidoking.
- Gengar has ghost type coverage as well as strong moves Shadow Ball and Dark Pulse.
- Nidoking has ground coverage and learns Thrash, Earth Power, and Megahorn, which are all powerful moves and Megahorn gives you bug type coverage.
In-game team Pokémon are generally not as carefully selected and trained as competitive team members, but these two are great choices for type coverage and power.
Personally, I'd also replace Fearow with a rock type Pokémon such as Corsola or perhaps dragon type Dragonite or fighting type Machoke. All three provide extra coverage combined with powerful moves. Also, when you get the legendary Pokémon, they'll make great additions to your team.