Some people go on & trim to 'ideal angles'. For eg. a German vet called Hiltrud Strasser preached that dorsal toe angle should always be 45 degrees(fronts) and hairline should always be 30 degrees. I don't believe this is a good move. Too many exceptions in 'the real world', for one. But there are a number of angles & measurements it's important to understand & consider...
Sighting side-on, the dorsal(front) aspect of the *bony column* should align - as HLG explained, the hoof pastern angle should be a straight line. *But beware that the dorsal angle of the hoof wall may not reflect the angle of the bone inside.
Sighting side on, the hairline gives a rough idea of h/p angle, and should be around 30 degrees, relatively straight, sloping down to the (low) heels. *But beware that the hairline distorts easily & may be 'jammed up' if the hoof wall is peripherally loaded/imbalanced. If the hairline is a lot shallower(or even, Dog forbid, sloping DOWN at the toe) this is an indication of forward 'rotation' of P3.
The distal(bottom) surface of P3 from side on should be raised at the heel from ground parallel, by around 3-5 degrees. And the *live* sole plane and the collateral grooves should be reasonably equal from toe to heel. *But this is disregarding exceptions such as 'clubbed' feet, too sensitive heels which may 'need' to be a little higher, etc.
Fore feet have a lower dorsal hoof angle than hind feet. If this is not the case in a particular horse, it may be due just to hoof probs, but it is often(usually?) an indication of body issues.
Based on measurements of many mustang hooves, it was found, by Ovnicek & Jackson(going off memory, don't quote me on actual numbers) that the *average* (meaning normal, but not all) dorsal hoof angle *of those horses* of fores was somewhere between 44-48 degrees & hinds were between 48-53 degrees.