I have always known a lot about the QH b/c i've been riding mainly them for about 11 years. and from what i read, you know quite a bit as well?? When i got my first horse, i wanted a challenge, so i went to this lady who had never fed them in her life (the horses were living off grass) and she didn't even know the difference b/t sweet feed and pellets....yikes!!
But anyways, i would go with the breed that you feel the most comfortable with, and QH are very versitile!! Just spend some time with the horse before purchase, maybe lease it out for a week before?? and just get to see how it's trained, and how he/she moves while riding, and that way you will get a good idea of what the everyday will be like.
Good Luck!! and HAVE FUN!!!!!