I'm seeing lots of bad advice in here. I think 2h from horse is better than 1h, and more useful on the ground as well.
A shield is not necessary for riding a horse (although I really like it for blocking projectiles, protecting you from a couched lance, or when dehorsed it allows you to stay alive longer...but it costs skill points that will limit your attributes). Do not drop athletics. Always max out your athletics, power strike and riding. I prefer to then max WM (you do more damage, pay less upkeep on weapons, and swing faster), others will swear by putting points into IF instead of WM. Don't go more agility than the horse requirement that you want to ride.
That's the first step is to pick what horse you want, as a 1h/2h I'd suggest going with a 5 riding horse so you can get more power strike. I'd suggest going 24/15 (basically giving up ironflesh for 1 one more power strike).
If you're using a shield, then I'd always do one of these 21/15, 18/18, 15/21. If not using a shield convert more skills to attributes and go 24/15, 21/18, or 18/21 (at level 30).
I'd suggest this build for you:
Level 30
Strength: 24
Agility: 15
Hit points: 59
Converted: 8
Power Strike: 8
Athletics: 5
Riding: 5
Weapon Master: 5
Otherwise you could go 21/15 and put those points you converted into IF (but I'd prefer to do more damage than take more damage).