I'm not sure if you would use this for competitive purposes, but ingame this works well.
Starter - Oshawott - Dewott - Samurott (Water Type)
Moves - Surf, Ice Beam, Hydro Pump, Revenge
Surf because it has a good base power and gets a STAB due to it being a water type move
Ice Beam to combat any grass types that might appear and is good against Flying and Dragon types as well.
Hydro Pump as it only attacks one Pokemon, where as surf hits everyone, so if in a double battle, you don't hit your partner, plus a STAB due to it being a water move
Revenge to hit any steel type Pokemon, and if damaged before, the power becomes 120.
Second member - Riolu - Lucario (Fighting/Steel)
Moves - Close Combat, Swords Dance, Psychic, Bone Rush
Close Combat as it has a high base power and with the additional STAB, makes for a pretty good move. Defence does fall but shouldn't be a problem if you keep speed up.
Swords Dance as it will further heighten Lucario's already decent attack.
Psychic to deal with any poison types as, though they can't hit you, still need to be taken care off.
Bone Rush to deal with any Fire type Pokemon, as fire is a weakness to Lucario.
Third Member - Mareep - Flaaffy - Ampharos (Electric Type)
Moves - Discharge, Signal Beam, Confuse Ray and Power Gem
Discharge - Ampharos specialises in Special attack, and with the added STAB and the fact discharge has a high base power, it can make for a good move. It hits everyone though, so be careful using it in double battles
Signal Beam - A bug type special move, it can take care of any grass types you encounter, and has a pretty good base power as well.
Confuse Ray - Because it's fun watching the enemy hit themselves from time to time, and plus may give you a few free turns to take out your opponent.
Power Gem - A rock type move with good base power, good against any fire types and good to mix up some move types.
Fourth Member - Pidove - Tranquill - Unfeazent (Normal/Flying type) (Try and get one with Super Luck ability, heightens rate of crit hits)
Moves - Fly, Steel Wing, Roost, U-Turn
Fly - Not only good in battle, but useful on the field as well. Has good base power and gains STAB due to it being a flying type move
Steel Wing - Hits Rock and Ice types well, so that covers weaknesses, and has pretty good base power
Roost - Mainly to recover health. If you don't want roost, use Return, good base power if your Pokemon love you.
U-Turn - Ideal to inflict damage and switch out to a stronger Pokemon if needs be.
Fifth Member - Growlithe - Arcanine (Fire Type)
Moves - Flare Blitz, Extreme Speed, Wild Charge and Toxic
Flare Blitz as not only is a powerful move, you get a STAB due to it being a fire type move. Highly recommend this move.
Extreme Speed has a priority of +2, and hits hard, so good for dealing that sure fire last hit
Wild Charge as it is an electric type move, working well against any water types, and it has a good base power
Toxic to poison the opponent and deal a lot of damage over time
Sixth Member - Petilil - Lilligant (Grass Type)
Moves - Energy Ball, Sleep Powder, Hidden Power (Fire), Giga Drain
Energy Ball is a great special move, with a high base power and STAB from it being a grass type.
Sleep Powder because putting the foe to sleep is always cool
Hidden Power (Fire) Because you need to have something other than grass type moves, otherwise an Oddish could probably take you out
Giga Drain to recover your own health while taking away theirs
Any Criticism welcome, as I said, I'm not sure about Online battling but this team hasn't failed me yet.