I say breloom since he has spore, one of the best moves in the game and he also got that 130 atk which is quite deadly for a mushroom kangaroo. Even though all his other stats are pretty below average, spore, his ability and his 130 atk stat makes up for it. Theres a reason why he is ou and shiftry and ludicolo is not. Breloom can be used as a subpuncher(Which I personally use) or you can abuse him with technician. I personally think the subpunch set works best since he really cant do much without hiding under a sub with those frail defenses. But overall I would say he is the best because of spore and his 130atk stat and him being able to use focus punch effectively.
Shiftry can be used in the sun alright but I personally dont think its nothing to compare to brelooms 130atk and spore. And he only has 100atk or 90spatk if you want him special but either way, he has to either set up swords dance or nasty plot to sweep which is a little hard with his bad defenses. But for breloom, he really doesnt need to since hes already got that destructive stab focus punch along with 394atk.
Ludicolo has great typing and stabs and can be used in the rain effectively as a sweeper but 90 specialatk isnt too much to sweep and gets stopped often