Who to buy?

is a weak jungler.

if you want cc go with naut. I like both of them but prefer naut because he can live longer and has great cc for team fights.

I wouldn't cast aside - one of the most exciting bruisers in the game that can tank also. is one of my perennial favorites though.

I think it depends on your definition of fun is...If you want something with some skill shots and helps the team be tanky, then mao. If you want to land one spell, then smash someones face in and stand in the way then pick naut.

Side note, if you pick naut remember you can auto-reset with his W. :)

is a pretty good support too.

Nautilus has some really good lock down and can be deceptively tanky. His anchor allows for some decent mobility for his otherwise slow move speed. He kind of lacks damage though and sucks on his first clear. Nautilus can also go support, top or even mid lane and can be built a variety of ways. Maokai has better sustain and a great first wave clear. His E allows him to start blue buff or red buff and can clear fairly well without a leash, which is nice. His saplings give him much better objective control and his W allows him to get through walls. Maokai's ultimate is great at team fights but is mana intensive and takes some practice on its proper usage.

Nautilus is more fun but I have had much greater success as Maokai.