Which is more difficult for you front-end or back-end?

Which is more difficult for you front-end or back-end? And why and which one generate a better income?

I think neither of them is harder, it's all about experience. Frontent frameworks tend to change a lot. Backend technology is a little bit more long-lived but you have to learn more about things like webservices, architecture and so on.

I'd say income is based on a few facts like
1) Country
2) Freelancer or employee
3) Industry
4) Just coding or business focused
5) Technology
...

If you want to earn good money move to the US or Switzerland, get in a high paying niche like ABAP and work as a freelancer for a big company with deep pockets.
Don't work as a employed PHP developer for a startup in India or someting like that.

Both of them pay well.

Just go with the one that u like the most and with technologies that are going to last long

Neither.
An artist cannot be a novel writer and vice versa. And both do pay well if you are good at them.

Both are or if you have enough interest to learn of leave the game