Everyones situation is different.
I don't use Windows, so Edge/IE is out of the question. I dont own a Mac, so Safari is out of the question.
That leaves me with Firefox, Chrome, or about 100 other less known browsers.
Mozilla is actively working towards a secure, open platform for developers and users alike.
Google is developing a browser because they are fixated on controlling and collecting data on their users.
On the operating system I use, Firefox is compiled to my system hardware (CPU architecture and features) making it highly optimized and very speedy. In fact, I've never experienced a crash I didn't cause myself (I develop web applications). I regularily monitor the RAM usage, and even with 10+ tabs open I never see Firefox use more than 500MB.
The few times I've used chrome, I have found it to be slow and bloated on my system. Not being able to compile it to my CPU arch and features makes it slow as it is compiled with the least optimized features so it runs on more hardware.
I am aware of chromium and I do compile it to my hardware, but firefox still outperforms it on my system... not really sure whats going on there.
I trust Mozilla a hell of a lot more than I trust Google, and due to my great experience with Firefox, I use will continue to prefer it in the forseeable future.