Play whatever you want. Some things are going to take more time when it comes to you feeling comfortable, but if you actively try to get better, the tank you enjoy the feel of will serve you best. Additionally, tanks balance is insane right now.
My opinions massively differ from others, and thats becuase the inroduction of real talent trees has created playstyles for some specs that differ from what people are used too. Currently i would say:
EASY LEARNING CURVE
Warrior, Paladin
INTERMEDIATE LEARNING CURVE
Death Knight, Druid, Demon Hunter
HIGH LEARNING CURVE
Monk
Warriors are very simple, in a good way. Sblock and IP are strong and easy to keep up, the rotational buttons are few and far between. Theres a ton that can be and shoulded be added on from talents from 1 min cds to a swiss army knife of CC, but at its core its a tank that with even basic understanding, is very durable.
Paladins are similar. Press your buttons on CD, spend HP on sotr, rotate defensives, and your in good shape. They occupy the low skill floor - high skill ceiling spot they usually do. Plenty of utility to make use of as well as being a tank that can essentially trade in durability for damage like no other.
Blood is historically the “casuals consider it easy, hardcore players consider it punishing” tank due to the nature of its design. If the content never hits that hard, than you can be hohum with your healing and it doesnt matter. When its tough, one bad deathstrike can snowball into a quick death. However, the current meta build is very passive, and Blood Shield is in a really good spot, so naturally resource management is not as punishing.
Bear is normally a great beginner tank due to Ironfur having no CD and Thrash + Swipe making AoE pulls more forgiving. Currently though, they are far more reliant on self sustain, needing to track wildfire, moonfires on all targets, well-honed instincts and regens + renewal to make sure they can recover. They unironically have some oldschool blood dk vibes atm.
VDH is the definition of nuanced. Not a lot of buttons, and they often feel like a DPS with tank abilities bolted on, which means thkae tank abilities need to be used with care and precisiobm Frailty takes practice to get the most out of, Fiery brand build is punishing and Demon spikes uptime is awkward, especially if your not running Feed the Demon.
Monk is objectively the hardest. Survivability while not bad, is extremely punishing, sustain is limited, timing brews and defensives is paramount, the amount of buttons will test your keybinds, and optimizing cc and utility is really important. Ton of fun though, and if your a player who can stay calm pressure, youll find Brewmaster is actually in a pretty good spot.
Play what grabs you, otherwise Warrior or Pali.