First pick would prolly be sylveon, kelfki, whimiscott, togekiss/diance, azu... i dont think i need to bother listing sets as they are all fairly well known
...i assumed you were dual typing, as for strategies i cant simply name them as they depend on the battle itself lol you could use kelfki as a prankster screens setter...sylveon as a wish passer...whimiscott as a stall, togekiss as u hax god....diancie as a speed sweeper, azumarill as a belly drum sweeper...there are many common sets for each of these mons and how strategic you are with them is up to you