I personally use LMMS though I don't know if I would say that it is the best, I find that once you figure out some of the quirks/subtle parts of it that you can really do a lot with it. I also like the set up with how it will divide into measures for you but also let you know the time ect. and it supports a wide variety of vsts and effect plugins. Definitely a good option for someone cheap/poor like me.
I also tried Reaper once, I didn't like it, and for some reason the connotation of Fruity Loop's always made me shy away from it. Plus why pay when I can get something that does the same thing for free?
edit: fixed typo