Klefki or ferrothorn

So if I do finally get that ralts I was thinking about masuda methoding another member for a team I was thinking about a set up pokemon but which one klefki or ferrothorn

It depends on what set up. I prefer stealth rock over spikes because it hits all pokémon, except for one with certain abilities. For stealth rock Ferrothorn is the one, spikes is Klefki better.
Ferrothorn is bulkier overall and also has excess to leech seed to heal and strong physical moves.
Klefki has prankster, can set up screen and his best offensive option is foul play.
Based on these factors you decide which one you want.

Thanks I'll take those points into consideration

No problem