prot paladin if you want to have fun, and concentrate on everything except tanking (i.e. positioning, dps, heals, dispels, boss abilities, interrupts)

feral druid if you enjoy a "Challenge" and want to spend more than 1/4 of a brain tanking

seriously, pally = ezmode tanking, especially on a shaman team with no CC, you will want good multitarget threat, which paladins excel at.

I personally use this macro for my main tank button (keybound to my shamans' lighning bolt button):
/castsequence reset=10, Seal of Righteousness, Holy Shield, Judgement

I click consecrate whenever i feel it's neccessary.