-> Seeing that now we have up to 20 + legendaries ... It's gonna be hard to choose just 3 or 4 to complete your team (saying that you have 3 or 2 non-legendaries).... I'll go with:
1) Lugia (one of the most powerful and complete legendaries out there... it can learn from fly to swim, aeroblast to hidro pump...and it has one of the most balanced stats taht you can find out there).
2) Kyogre ( monstrous Special Attack... and I know that in the anime series it says that Kyorgre and Groudon will fight for 1000 years or so... but I think that this is the only pokemon that can beat from Articuno to Deoxys IF WELL trained... a most-needed pokemon).
3) Mew ( from my personnal oppinion, Mew is not THAT powerfull, however it it the most unique character and elusive, because of ther fact that itself can learn EVERY single type of attack, and that is useful, because you can adapt Mew so it can have the type of attack that are less present in your party).
4) Ho-oH (I choose Ho-oh because of its fire-type moves and even though it is psychic, it is the most different from all of the others in terms of type, stats, and moves, that makes it a fine adition).
5) Rayquaza (to me, the second most powerful legendary out there, and the fact that this is 1 of 3 only Dragon-types, makes it even more valueble, its OUTRAGE + its Special Attack make it a deadly foe to ANY pokemon)
3) Mewtwo ( who else?... they have tried to duplicate it with Deoxys, tried to create 2 with the same power in Lugia and Ho-oh.... but this is simply the most powerful force that you can have in your party, the perfect "last resort" and having it, gives to ANYONE inmense confindece dutring a battle...it doesn't matter how many pokemon Nintendo creates...This one is SPECIAL all-around... PS: remenber how hard it was just to simple beat it at Pokemon Stadium 2 when you had 6 pokemon against it...:)
Or you could not use legendaries and actually use skill for a team.
Also, welcome to the boards!
I'm just going to run off my favourites regardless of whether or not they're good components for a team.
Dialuge
Lucario
Lugia
Deoxys
Suicune
Rayquaza
Badass.
Mewtwo (heck, my ideo game name is MEW2)
Rayquaza
Kyogre
Groudon
Lugia
Ho-oh
I wouldnt use a whole team of Legendaries. Sure, if they are all level 100, they will own anyone they go up against, well, any computer player anyway. But, if I had to choose, I'd go with these.
1. Mewtwo
2. Entei
3. Ho-Oh
4. Lucario
5. Latios
6. Mew
Rayquaza
Lugia
Entei
Mewtwo
Grouden
Deoxys
I don't know much about the newer Legendaries, but as far as just how they look, I could easily pick 6 :
Rukario
Deoxys
Articuno
Registeel
Groudon
Mew
1. Kyogre
2. Mewtwo
3. Zapdos
4. Rayquaza
5. Raiku
1. Mewtwo
2. Mewtwo
3. Mewtwo
4. Mewtwo
5. Mewtwo
6. Kyogre (in case of annoying dark pokemon lol)