Full quarter horse bars means the width in the front of the saddle tree is around 8″ wide semi quarter horse bars are usually 6.5 depending on manufacturer.
I enjoy my bob marshall treeless saddle it is a 14.5 and my english hunt saddle is a 17″
I also love love the way my Pro Rider barrel saddle fits just about every horse i have put it on includinv high withered horses. It is also a 14.5 seat.
The barrel saddles and treeless saddles will give you a more close contact feel and will weigh around 25lbs. A trail saddle will be between 30-40 lbs and will not give you the close contact feel.
My M Toulouse saddle is a 17″ and i feel most comfortable in a 14″ or 14.5″ western saddle.
I hope this helps!