In AMHR you got 4 main driving classes.
There is Western Country Pleasure Driving. Fairly new class, it was introduced back in 2007 I believe. Horse's head and neck is level, more of a sweeping trot, not the knee action you see in the other classes. You will also see many people wearing western clothing and some horses are in western type harnesses. This is my Hall of Famed Western horse.
And you got Country Pleasure Driving. More animated with knee action, horse's head set is up and tucked and still be a pleasure to drive. Here is my Country Pleasure Hall of Famer.
Then you have Pleasure Driving. The horse is animated with knee action level or above level, horse's head is up high, lots of lift. You will also see often your pleasure horses are hotter to drive. This mare has her Pleasure Driving Hall of Fame but now your Pleasure horses are even more animated then what she is now, that is why she has done so well in Country.
Finally you have Roadster. You see people in silks, you see horses wear bell boots most of the time to protect their feet. It's all about the extension and speed. Fun class! My Roadster Hall of Famed horse.
You also have other classes like Park Harness which not a whole lot of horses compete and some aren't even your true "Park" horse. Those horses are nothing but up and down action to them, more animated the Pleasure horses. You also have Draft, Light Harness, Fine Harness. Here is my two in Draft.
Another fun class is Roman Chariot.
My advice is watch the AMHR National show online which starts next week, it lasts from September 4-14. Here is the link:
http://www.iequine.com/events/2014/09/amra-national-championship