Who is the hardest hero to learn/use?

Quite good he says :D After +2k games of dotka I still haven't seen a player that knows how to deal with this hero yet, but I can easily see why his win rate as well as popularity is one of the lowest in the game. To do something with this hero you need to pass through learning stage that takes really big amount of games with like 20% win rate, unless you have really good teams that carry you or are kinda above average player. But then after learning stage there comes that moment where you can already play this hero and your win rate as well as mmr goes up very steadily, many players just give up during 1st stage.

It's really a toss up for me. Invoker and Earth Spirit both require twitch reaction times and the memorization of ability combinations in order to be played to their fullest potential. While Invoker may have a larger quantity of abilities at his disposal, the abilities that Earth Spirit is equipped with require more skill are much harder to land on enemies. I'd say with the arrival of 6.82, Earth Spirit gained a new level of depth after gaining access to the new ability Enchant Remnant. This allows for you to turn both allies and enemies alike into Stone Remnants, opening up a whole new list of ability combinations that need to memorize. As of the new patch, I would definitely say that Earth Spirit has become the most challenging hero. Micromanagement becomes easier with time, and Morphling was never all that challenging to begin with. Earth Spirit, however, requires skill and dedication to play. As much as I do respect Invoker and Invoker players, I can say out of personal experience that he becomes much easier to play after you learn the ins and outs of all the possible combinations of Quas, Wex, and Exort. Not to seem rude, but I have indeed written up a guide for Earth Spirit designed specifically for those learning how to play the hero and those looking to get better. There are also some helpful tips and tricks thrown in the mix for the more experienced player looking to take their Earth Spirit game to the next level. Here it is:

http://www.dotafire.com/dota-2/guide/the-perfect-spot-mastering-earth-spirit-10619

Enjoy learning the new and improved Earth Spirit as of 6.82

It's really a toss up for me. Invoker and Brewmaster both require twitch reaction times and the memorization of ability combinations in order to be played to their fullest potential. While Invoker may have a larger quantity of abilities at his disposal, the abilities that Brewmaster is equipped with require more skill are much harder to land on enemies. I'd say with the arrival of 6.82, Brewmaster has become the most challenging hero. Micromanagement becomes easier with time, and Morphling was never all that challenging to begin with. Brewmaster, however, requires skill and dedication to play. As much as I do respect Invoker and Invoker players, I can say out of personal experience that he becomes much easier to play after you learn the ins and outs of all the possible combinations of Quas, Wex, and Exort. Not to seem rude, but I have indeed written up a guide for Brewmaster designed specifically for those learning how to play the hero and those looking to get better. There are also some helpful tips and tricks thrown in the mix for the more experienced player looking to take their Brewmaster game to the next level. Here it is:

http://www.dotafire.com/dota-2/guide/brewmaster-the-drunken-balla-8703

Enjoy learning the new and improved Brewmaster as of 6.82

you have got to be kidding me, brewmaster is easier than morph, I mean really essentially your contribution is to blink in press R and tab a few times and then just hit things.

Earth spirit you say....nope not really that hard once you get some practice.

Meepo...just set up some micro keys and get some experience, not huge.

I would say invoker is the hardest, you might say that being able to pull off all these fancy refresher combos and that is the most you can do, NOPE NOPE NOPE. To skill cap an invoker you need to keep the cooldown of every spell in your head, be constantly invoking every time off cd in fights. For example your refresher combo yes say your favorite is (pre-prepare forge spirits) tornado-emp-meteor-refresh-emp-tornado-blast. But that's all very well but there is follow up when you blink/force inice wall, cold snap, alacrity by which time forge spirits and tornado are off cd and your casting them again while sunstriking someone running away.

Have I made my point?

Beech please, that's pub way of playing Invoker - all these sick refresher combos that will happen maybe once per 100 games. Just look at pro players playing invoker during pro matches - all they're doing is sunstriking other lanes, while pushing 1 lane with midas, necro 3 and spirits. Not a single time they've used their fancy combos because it's not effective. Get over it, higher level invoker isn't about fancy combos, he's about high right click damage, high pushing power and has always team built around him + carry that benefits alot from alacrity.

Would replace Morphling with Luna as she is by far the hardest hardcarry to play well.

May I ask why?

No escape whatsoever, squishy, no ability to get into someone's face and kill him quickly(com[pared to other heroes), a melee hero, though damage block and bashes work for ranged, situative ult. Quite a lot of traits to frustrate a new player.

I don't understand why people only think about micro skills or timing spells when talking about a "hard" Hero: to me, multi-tasking is what makes a Hero really hard to play. For example, as an Invoker, you only need to care about your two spells in your skill bar, while as a Meepo you always have to rotate between jungle camps with your secondary Meepos and find openings with your main one. I always see players going around with all four or five Meepos together: this, people, is not the way to play him. And if you are facing a team with good warding, they will eventually gank your jungle Meepos for sure, so you need twice as much awareness.

I've already talked about Invoker, what about Earth Spirit? I don't find him that hard to play, but it depends on whether you want to master him or simply be good at him. Mastering a Hero is generally hard: as an Earth Spirit, as soon as you learn the main combo(s) you're fine, the problem is pulling them out in any situation. Still, that's not even comparable to playing well as Meepo in my opinion.

Chen, on the other hand, is very similar to him: I really love him (I played like 10 games in a row as a Chen once), and every time I played him I always forgot about something, whether it was warding or buying items or teleporting when needed. Using the persuaded creeps isn't that difficult once you get the hang of it, but doing it when you're busy (warding, activating your ultimate at the right time et.) is kind of hard. Not as hard as playing Meepo, in my opinion, but still very hard.

What about Visage, who you didn't even list? Farming and contemporarily split pushing with Familiars requires map awareness and decision making, and playing a good support role at the same time - much like Chen - isn't that easy.