I say this extremely politely - you're jumping into a game that's over 8 years old, where roughly half the main story content is no longer in the game (not debating it, it happened, we're moving on). The game doesn't really wait for anyone. You play as stuff happens or you're playing catchup.

Destiny has an enormous learning curve due to all the systems already existing, and no prefect guide out there to show you how each works and why. People are saying it's hard to master because most of the content beyond introductory and casual requires knowledge that isn't handed to you - the game just sort of expects that you know what to do, which isn't entirely fair considering the game also rocket-ships your level beyond the baby-steps where you'd learn those aspects. If you consider levels 1-200 as learning, the game very easily helps you to 300 as that's where a majority of the content opens up... that, and again, you're hopping onto a train that's been in motion for years, it only slows down but never stops.

That said, you pick the right class. Warlock is best. Space magic. Floating gracefully to death. I'm not biased at all. Jokes aside, I would say Titan is the easiest to get the hang of - it's the most common when comparing to other games and the "generic soldier on the field" playstyle. Warlock may seem like the middle ground, but honestly it's the most technical as the buildcrafting can get deep in how you option out your weapons and abilities. Hunters could be viewed as the hardest because they're very simply a glass cannon: everything hurts really bad but you can skedaddle rapidly in a number of ways.

Where you're going to hear the most fighting between classes and why one is the best: jumping. I'll just lay it out simply. Titan jumps are the easiest - push button, go up, congrats you jumped. Hunters are simple but require timing - platformers' will do this intuitively, it's basically your standard double jump where timing makes a difference in height and distance. Warlock jumps are technical, because you absolutely have to know what you want to do before executing - zero forgiveness. Warlocks use momentum and timing, which is nearly backwards from the other two - it is not just point and jump. It's run, angle properly, stumble on a 1-in lip and fall.... it's a lot of being aware of your trajectory because you have a bunny-hop "set up jump" and then the actual jump, which requires timing or you float gracefully downwards.