I'm probably gonna go with shen, mundo and alistar.
Nautilus can work but lane nautilus isn't as strong as say "shen alistar etc" and in the jungle he gets crippled by losing blue and if the enemy team knows its a jungle nautilus they will nearly always invade and ward blue, so hes pretty risky nowadays.
Shen and alistar offer a lot of utility, shen is better as a solo top tank, alistar as a bot tank/support. In terms of tanking damage alistar is the best tank, ulti, high base stats etc. In terms of laning phrase its around even, since shen has the global ulti, so he can constantly pressure lanes and alistar has a heal and headbutt pulverise which is amazing for making plays with the ad and jungle. Teamfights its pretty hard to compare too, mostly depending on the team comp, since a good shen can sometimes taunt more than one person and initiate amazingly well, although it requires a lot of skill and luck, and he has the amazing ability of protecting the carry with his ulti during teamfights, which is gamechanging. Alistar again is an all round beast in teamfights, reliable and amazing initiations, can tank a hefty amount of damage too with the ulti and innate tankiness.
I put mundo on the list because he has the potential to snowball like a ***** from the jungle and practically become unkillable after a certain point, because of his regeneration abilities and a ****ing amazing low cd ultimate, although he lacks cc.
Personally I feel like amumu needs a few minor buffs to put him on level with the other tanks and being ap and all doesn't help, plus his ulti is amazing, but its cd is crippling and he can get cc locked very easily, whereas mundo, shen and alistar have an easier time escaping. Malphite is very very good but honestly I just don't think he is on level with the others and apart from his massive early game utility I feel like he's outclassed by the others, even if his ulti makes his teamfight presence deadly. Ohh and rammus atm is pretty gimped so yeah thats just my thoughts.