Thinking of starting tanking, need advice.

[VenKitsune]

Easiest: DRK
Mild: PLD
Hardest: WAR

As for "Fun"
PLD and DRK.
PLD is a bit more of a challenge, but still plenty easy.
DRK is straightforward. (I actually find DRK boring as heck, but there's quite a few people who find the simplicity of DRK fun.)

PLD is the best in pretty much any situation, be it MT, OT, ease, fun, etc.

The only exception is lower levels, where maybe WAR is more fun, since it has berserk, and PLD lacks the fun abilities till closer to 50+

I really, really wouldn't call DRK easy at all. At endgame for a seasoned tank both PLD and DRK are fairly simple but DRK has a lot more options in regards to how they spend their MP and MP management. The only reason WAR is so difficult right now it because it's a little clunky and in all likelyhood we'll be seeing some changes in the coming month to make it both more fluid and more viable.
PLD has and always will be the simplest of the 3 tanks in the game.

PLD main here but i played all of them during HW.

Pld is the one that teaches you tanking the best in dungeons and instances imo, and is in a very good spot rn so i def recommend it but the other tanks are not bad either even if they might lack raid utility rn, this will hopefully be fixed soon

My advice would be 'try out pld and see if you like the principle of being tank' (don't be discouraged if you lose aggro sometimes esp before u get tank stance) and if you see that you like doing it, you can try the other classes and play around with them

Pretty much this. PLD is excellent at teaching how to tank as up to lvl 54 or so you only have one single target combo, and 2 aoe skills which have different functions. Meanwhile WAR is about managing the beast gauge and using Inner beast at the right time to mitigate stuff, and doing loads of damage when you can afford it. DRK is more about MP management which adds a great deal of complexity to the class.
Back in 3.x i would argue that DRK was the hardest of the 3 tanks but now i'd say that WAR has taken that spot as i mentioned because of its overall lack of fluidity which will likely be fixed. Again like i said in about a months time or so i'd wager that DRK/WAR will be the most complicated to a similar degree where as PLD will be the simplest, this is how it's always been and forcing people to swap which tank they play the most because they want to play the simplest for example is bad game design, it will be fixed. Ofcoure this is all about endgame and as far as leveling goes either of the 3 tanks are completely fine. i suggest OP just picks the one they like the look of most and look up some basic tanking 101 guides.