I'm personally definitely not a fan of GIMP at ALL. It's what I first used when learning how to draw digitally and I would never suggest it for anything serious. I use Paint Tool Sai, which is my personal preference, but it does come at a price. A friend of mine transitioned over to clip studio paint for a little while since she was using a Mac computer, and there isn't a sai download option for Mac computers. Of course, clip studio paint is also not free, but she very much enjoyed the program while she was using it (she has since returned to paint tool sai). She did use firealpaca for a time as well, which is what I suggest for you if you would rather not purchase a program c:
Do note that I am an artist by trade. I'm not the greatest artist, but I do have some experience and I hope this is helpful for you! <3