It is a very broad question without much of a context, I will try my best to answer.
The short answer is it depends, because every person is different, for example I liked Mechanical Engineering because I like to see, touch and feel things. When I am able to see I am able to understand things better, I am able to think other perspectives better, I am able to think about how I can improve that better, I think that is because that is the way I was brought up. During my vacation days I spent time with my grand father hammering hot iron in his workshop, I have spent time carving and building toys with wood and I enjoy making things. And when I started building Software, it was difficult because I wasn't able to see the programs I was writing, but eventually I figured it out, the reason it was difficult initially because I had not done it before, had a kid that has played with a lot of video games been given that task of writing a program, for him it would have been much easier because he is already used to a lot of virtual things.
I think it is all about comprehending, what is that you are able to comprehend very quickly? And that depends on your past knowledge and comfort with the things you have done in the past.
So it all depends on where you are coming from. I would approach this not from a point of hey, which one is easy or difficult, what makes sense for me to spend my time, what am I going to accomplish in that specific field, if you get a context around why you are doing what you are doing, what inspires you to do that, that would put in a better place to start with and you would make the right choices and also would be lot more fulfilling in the long run.
Also check out my other answer in contextual learning that would help as well
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