How many legendaries to keep?

I personally keep one of each legendary with the best IVs I can manage to find. I don't really find it appealing to use more than one of the same legendary Pokémon.

At least 3, 1 per moveset, every 96+.
I'm keeping 3 Articuno, Zapdos, Moltres, Entei.
4 Lugia. 6 Suicune (different HidPow).
5 Raikou (all 96%).
4 Ho-Oh ?

I keep the 3 with best IVs of each one, no exceptions. Only had to trash one 90+ legandary because of this I think. I still don't feel ok powering up more than one but I want to keep more just in case I change my mind. Also it's nice to see rows of three.

I'm keeping up to three, but only powering up one for now. I'll probably make an exception with Mewtwo (and possibly Ho-Oh), and power up more than one, because the different movesets have very different uses.

And although I will only keep up to three of each, I will only transfer legendaries during double candy events.

6 of each!

Some of these answers were funny considering trading is eventually going to be a thing