If you buy a highly trained, extremely responsive horse who operates on a hair trigger, you will not be able to handle him. Riding him will not be fun or safe. It would be like giving a Ferrari to someone who can barely drive. Here again, decide exactly what you want in your first horse, and do not overestimate your capabilities. Stallions, or breeding age males, are not suitable for first-time horse owners.
Some horsemen swear geldings are more reliable in disposition and attitude than mares.
However, some pe ple contend that mares make more willing, responsive mounts, yet others consider that geldings are far steadier to handle and ride on a daily basis. The choice is yours. Should your riding plans include another, more trained horse in the future, once you have mastered the basics of horsemanship, you may have considered the later possibility of raising a foal from your first horse. In that case, you know what you want a mare. You aren't wasting time test-riding geldings.