It will feel like some one is pushing on your teeth. The brackets stick out a bit from your teeth making it feel like you have a full mouth of metal, big lips and your bracket may rub against your lips feeling again like a metal file.
While some breeds may be more suitable than others for a beginner rider, there are always exceptions to the rule. Quarter Horses often make great beginner horses because of their even temperament, but some can be quite hot or energetic for a beginner.
Don't worry if you see some of the horses listed as both a stamina and a speed source (like Princequillo). The stamina sources are lines we can build into the far reaches or middle of our pedigrees to bring more stamina to our sport foals. As I said above, America has produced 25% of the world's staying bloodlines.