As a fellow newbie, I've tried Red Mage, Machinist and Ninja at 70+ and some others at varying levels and my pick for easiest would be Machinist. The ability to continue DPSing while moving is a big plus in terms of 'forgiveness' and the rotation is fairly straightforward. It also has a lower button count compared to some of the other classes which make the learning curve all the easier.

Perhaps its simplicity may get tedious over time and you'll find yourself craving a greater challenge, but that's the beauty of FFXIV and its multi-job system. As for myself, I'm still loving my little Machinist and taking it as my main into Endwalker. People can mock the choice all they want, I'm having fun with my newbie class and I'm not a burden to groups trying to figure out overly complicated rotations, so that's all that matters to me ^.^

Regardless of what you pick, it needs to be fun to you. That alone will push you to hone your skills out of love for the job.