Environment VS Genetics

Sometimes you just have to wonder about some horses mental capacity and what their genetics has to do with it. I've got two horses here that arrived at almost the same time, were exposed to identical training, in the same environment. One is still in 'basic" training and the other has been ready for advanced training for more than a year. Topper and Ladybug were both purchased as weanlings and both arrived about the same time when they were both between 7-9 months old. Both of them had been halter broke, trained to lead and load in a trailer, trained to stand tied and to pick up their feed for cleaning and farrier work. So they had basically the same amount of training when they each arrived. They got an equal amount of training after they arrived because they I worked them the same. Yet I've had to hire a professional trainer to work additional with Topper while Ladybug has just breezed through every task I've ever put in front of her. 

Topper still needs more work before she's ready for advanced training. She seems to take longer to learn new things and she seems to get frustrated more easily. Ladybug on the other hand has rarely acted frustrated and never seems to forget anything. At  point I'd even been able to leave her in the pasture for almost a full year with out being ridden and brought her right out fresh from a layoff and picked right up where we left off a year previous. That year I let "The Bug" rest, I still had to work Topper. 

Topper is a beautiful horse, totally gorgeous in my opinion and she has a much stronger championship blood line that makes her more marketable to people interested in showing or breeding for show. Ladybug's pedigree is not so strong and most people don't think she's the "pretty" one. But those brains she has overpowers any pedigree going. In my opinion, Topper's not the mare I'd really look at breeding unless I found a stallion that was EXACTLY like Ladybug in attitude. Ladybug on the other hand, I want continually to raise horses like her. Horses who learn quickly, perform to the best of their ability at all times and who really are a pleasure to ride and work with. 

I know that this is not the result of environmental factors since the environmental factors were basically the same for the vast majority of their training. It has to be the result of their genetics.

Would you rather have a pretty horse that is difficult to train, or a not so pretty horse that is a dream to train or something in between. I know that we can't all have pretty horses that are easy to train so there has to be a happy medium.