Well, stat wise than Tangrowth is the best bit he has about 535, but then he has 5 weaknesses. Fire, Ice, Poison, Flying and bug. If you you're team is able to cover those than your good to go. He could also have a better nature. Like Calm or Sassy. His ability could be Leaf Guard and then you just use Sunny Day and you won't be bothered for five turns. It's vital to have another Nature that raises his Sp.Def or he won't last very long against a Special Sweeper.
Ludicolo has less weaknesses than Tangrowth and Shiftry, only his Sp.Def is good (in my opinion). If you are an EV Trainer than go for Ludicolo. His ability is also perfect ;)
I don't really like Shiftry, his defenses aren't that great. The only good thing about this Pokemon is his Attack. He might work as a Sweeper, but then you wouldn't be able to switch him in.
Go with Tangrowth.