Originally Posted by Speed Racer
You're asking a complicated question but expecting a simplistic answer, and it's not that easy.
It's not a particular breed that's good for a beginner, it's a particular horse. You need to look at temperament, soundness, training, and how well a horse tolerates noob mistakes.
Any breed can be good for a beginner, as long as you pick the right animal with the right temperament and training.
That being said, I'm a huge fan of laid back Arabs for beginners. It's hard-ish to find Arabians like this (it all depends on how they're trained), but when there's one that's calm, spook-proof, and sweet I really don't think you can get a better beginners horse. Arabians have enough smarts that they seem to understand what's needed even before their rider does and they generally have a very people oriented personality that seems to go over well with someone who wants to feel like they have a strong bond with their horse.
Of course, Arabians are totally not for everyone and many Arabs only have those characteristics (laid back, calm, etc) with a strong leader-type human and with a more laid back human, things go bad. But this is just my personal belief.
For instance (I'm an Arabian person and therefore have an Arab myself) my mare is one of those naturally hot ones. The kind that are all snorty and a little scary, but I've asserted myself as her leader so while she's still prancy and snorty, she's careful prancy and snorty. Like yesterday, I was kneeling on the ground next to her clipping her fetlock hair and she had her nose literally resting on the ground so she could watch me and make sure I was safe. She's just like that, my safety is #1 in her book so she is always making sure she's keeping me safe. I haven't ever fallen off of her either, there have been times when I've almost fallen off but she always figures out a way to get me back centered. Another thing I love about her is that she's a talker. She's always nickering, sighing, whinnying, whatever, at me and I find that super adorable.
I just love how personable she is with me.
Of course, I'm not a beginner anymore but she is my first horse. I do use her for beginner's lessons to kids, ages 6-13, and she's absolutely great with them too. Even on her prancy, scary days, she still puts the child's safety first and never does anything more than they can handle.