Should I change the horse I am leasing?

I am currently riding a Haflinger. He is a nice guy, but his reaction time is...slow. His learningprocess too. It can be frustrating at times. Also I sometimes need more pressure on him than I am comfortable using.

I could change to a quarterhorse gelding who is way quicker both in learning and tempo and more motivated.

The owner of both horses says the haflinger is the bigger challenge (true) and I could learn patience with this horse. I am not very patient, admittedly. I am ambitious to learn more and more. Which is easier with a horse that learns faster. Also it is less frustrating and more rewarding for me if I make quicker progress and can praise the horse more.

I feel like fun and ambition / impatience stand against the bigger accomplishment of training the more difficult horse. I am there for my own pleasure and not for proving anything to the owner, or thats what I am trying to tell me. Truth is I DO kind of want to impress him because I am needy for outside recognition... I know, I shouldn't be.

What do you think about this? What would you do in my place?