Welcome to Azeroth!
Bear.
By universal acclaim, Bear - aka Guardian Druid - is the simplest tanking spec.
It’s fair to say that in some patches, and in some situations, other tanks might be better for that situation, but overall Bear is the easiest to play.
That doesn’t necessaeily mean it is the one you will play best.
The one you play best will be the one you like most, the one that “clicks” with you.
But Bear is certainly the safest one for easier content.
You should watch some videos on YouTube from searches like
-
Beginner Tank The War Within -
Easiest Tank The WarWithin -
Tank Tips The War Within
and then something like
Guardian Druid The War Within
Druid is also an awesome class for soloing - on paper, it’s the best, so you also have that going for you. In your various shapes and specs, you have sooo many extras! Stealth in cat form. Instant mount. Dolphin/Seal form for breathing and breathing underwater. Ranged spec in Boomkin. Lots of self-heals available. Druid has it all.
The one potential downside is that your character is ALWAYS an animal rather than a humanoid, which some people find offputting. You won’t be seeing all that awesome transmog you collected. But if that doesn’t bother you, have a go!
How bad will they hate you? About 20%-30% of random people you meet in groups will will hate you regardless, unless you are a God Among Tanks. Actually, it doesn’t really rise to hatred - think of it as road rage. The will even rage when you do things right, if they don’t know you were right. They pretty much rage at anyone who doesn’t do what they expect. Bears have very thick skin - learn to use it. 
The thing to do when you hit max level is to join a guild or community that does group content together. There are many available, but finding a spot that suits you in one can be a journey.
Many Communities (distinct from Guilds) communicate mostly on Discord rather than in-game, so if you are familiar with Discord, look some up. There’s one called “WoW Made Easy” I’ve heard good things about.
https://discord.gg/Fj3EuN2XD7
You can join any number of these Discord communities before you even get to level 80, and get to know the people and the rules.
Please ask any other questions you have! 