This first set of brushes I either just use on Large paintings (24 x 30 and up) or in some instances I'll use them to blend two or more colors together. These range in size from one and a half to three inches in sizes.
This next set of brushes I use primarily for painting in large areas. For all of my temple paintings I used these brushes to paint in my sky's for example. The brush on the left is a new never been used brush. The brush in the middle is the same brush just four months of use. As you can see all of my brushes slowly spread out, no matter how well I clean them. From time to time I'll even use an ultra-sonic cleaning tool to clean my brushes. But in the end they all spread.
These next set of bushes are the same as the above brushes just smaller. I try to work with the largest brush I can get away with in an area so as to spend less time noodling away an area. Although recently I've tried using smaller brushes to improve the over all texture of my paintings. With all of my paintings which brush I use is really based mostly on how lazy I'm feeling and over all feel. Every artist has his or her own preference to brushes based on there own approach to painting. The only real way you can learn this for your self is to just jump in and start painting. I once had a dean of the art department at the University of Utah tell me that if you want to learn to paint, then just go and paint. The two best teachers for painting are Trial and Error. Experimentation is how I learned to paint ( and Greg Olsen's patience).
The last set of brushes are my Liner brushes. To the left is a new brush, the middle is one that has had it as a liner and the right one is one in which I trimmed down after it had spread. So that is the future of the middle one. I'm often trimming my brushes, especially when they start to spread out.