Lugia is A Tier on Smogon's in-game viability rankings, while Espeon is C Tier. Though Lugia is available later, it has more immediate power and excels against the Elite Four. By comparison, Espeon's frailty and Friendship requirement make it generally inferior to Lugia's bulk, strength, and matchups.
Further, I wouldn't recommend Umbreon in-game; it doesn't KO opponents quickly enough to be worth the time. There aren't any better Dark types, but you could try Haunter or Gengar if you really need to hit Ghost and Psychic types.
Lugia @ Choice Specs / TwistedSpoon
- Aeroblast (starting move)
- Extrasensory (starting move)
- Hydro Pump (starting move) / Surf (HM)
- filler
Replace Extrasensory with Psychic once you reach the postgame. Lugia has a wide movepool, so you can teach it whatever your team needs most.
HeartGold and SoulSilver In-Game Tier List (Smogon)