Well, I finally beat Emerald, and now I'm doing Battle Frontier and going back and beating the E4 for fun. It should be noted I play Emerald 386, not normal Emerald. My team is: (I just recently found out about natures and stuff, so I didn't really take those into account)
Milotic: Water Pulse, Surf, Ice Beam, Recover
Charizard: Flamethrower, Hidden Power Rock, Slash, Aerial Ace
Gardevoir: Psychic, Shadow Ball, Thunderbolt, Calm Mind
Salamence: Fly, Dragon Claw, Dragonbreath, Crunch (Edit 2: Whoops put Fly twice!)
Machamp: Cross Chop, Karate Chop, Low Kick, Rock Smash (Usually Revenge but I haven't made him relearn it yet)
Slaking: Slash, Strength, Slack Off, Earthquake
All are level 100 for Battle Frontier, and I'm also having my Milotic do Beauty Contests. About to take on the Hyper Rank. Wish me luck!
Edit: I'm considering starting Leaf Green and going Mono Water, but I don't think I have the motivation to do that, so I'm making a team on my Emerald 386 version.