It's all about what the specific project or client needs. We use online production music libraries which give easy access to a huge collection of different styles and genres, plus they are continually expanding, as the providers add more content.

Authentic sounding music with good production values in a variety of styles is what is useful from my experience. Last year I needed to use a lot of 'quirky', folky music (this is in an advertising context), but I haven't worked on any projects like that this year, so I guess it just goes to show that trends change quickly..

I agree with Mr. Bryant--I kinda need some of everything. I don't specifically use loops, so this doesn't directly answer the question...but it does depend on the particular project.