Spring-Summer-Fall I live in either Ovation or Tuff Rider ribbed breeches. The Ovations are a little nicer looking I think, the Tuff Rider ribbed breeches are a little more casual, but very cool in the hot weather. Both brands wear well, the Ovations maybe a little better, but for inexpensive breeches I’ve been satisfied with both.
For winter, nothing beats the Irideon Wind Pro breeches. They are wind/water resistant and fleece lined. They are flattering (don’t have that “shine” that a lot of fleece lined breeches seem to have that highlights all the details of what you wear under your breeches), and hold up really well to daily wearing, and can be thrown in the washing machine with normal detergent.
The Kerrits Sit Tight breeches… the full seat or knee patch part is a rubbery material… a friend of mine had a pair of the these, and they were very squeaky on her saddle, and they stuck SO tight that she actually got stuck half way on a horse! She went to swing her leg over the back of the saddle, and when it contacted the saddle, it wouldn’t slide the rest of the way over the horse! It was quite amusing for the rest of us, but she promptly got rid of those breeches 
For sizing, most of my jeans are a size 4 (like at Gap or American Eagle) and the Ovations or Tuff Riders I like in a 28 and the Irideons I get a small.