As one who plays both I use PLD more for primals and war for actual dungeons. PLD is much simpler to play cause it's a basic 123 it's pretty hard to mess it up as a healer you half to know the fights so you know when to buff a tank up especially on SCH so using that knowledge makes tanking simple cause you already know what to expect. you will take less damage on PLD cause you not only parry but block, war only parries. War has a great buff with inner beast and because of how wrath works now you can expend you stacks more frequently but will always be able to get back to 5 with no effort.
If your new to tanking in general I would recommend PLD it's easier to use and gives you more leeway to learn after your confident try War tho war is vastly more fun with the diff kit your given. Dunno if that helps