I'd like to think war and pld are like smn and blm respectively. They are both comparable and excel in different areas such as aoe and single target and are both "harder" than the other, depending on your preference. Imo PLD is the harder of the two since flash is your only enmity generator outside of CoS which is on a 30 sed cd. You also don't get access to Shield Oath, which is your tanking stance till 40 so you are learning to tank in your dps stance for a whole 10 levels, assuming you actually do dungeons and don't fate grind to 40.

For anyone who asks me advice on which tank to level and are serious about tanking, I almost always say PLD since they will be learning the foundations of great tanking and to not rely on spamming their aoes.