I don’t think there’s an actual answer to this question. It all depends on your style, ability, and time. Sure, it’s easy to say that one style is easier than others, but it depends on the person’s preference. For example, my personal preference is 2D Anime Art. I don’t do fanart, I like to draw my own characters. And I can’t just draw any old random side character, it has to be one that has a story or an interesting personality/past, and I use that as inspiration for the picture. For others it may be different. Whether you’re someone who draws for hire, or can just complete an amazing piece from the top of their head simply because they ‘felt like it’, all are important factors as to how easy or hard you found a piece to create.
It can be easy to get discouraged too. But don’t! One thing to keep you going is to keep in mind that there will always be someone better than you.Or people. And that’s no excuse to give up/be jealous/sob in a corner, no! You should congratulate these people and use it as incentive to improve your own art. Plus, if there’s people better than you, that also means there’ll be people that are worse too. So hang in there! Find your style, and keep moving on. And if you find an ABSOLUTELY AMAZING piece of work by an artists that’s been doing it for God knows how long and you just started, don’t throw down your paintbrush/pencil/graphic tablet pen just yet. Give yourself time to reach their level, or even higher. I’m still not quite at the level I’d like to be, but hey I’ll keep going til I reach it!
Plus, you’ll improve more every time, and I even have proof. This is how my drawings looked when I first started (and I was still proud of them)
Don’t give up!