AR10 is nice.. AR15 is alot more economical to build out and shoot as well. It depends how far you wanna reach out and the purpose of the rifle. For self defense and target shooting up to a few hundred yards, I go with an AR15, the best part is youll have alot of that cash available still for christmas!!
Now an AR10 would be more suited to you if you wanna reach well past that range and send followup shots quickly. Again, if you built it yourself, the quality control will be higher and you can still have some money left over for christmas!!
I personally have a Remington 700 R5 bolt action sniper rifle with a 10 round magazine. Although its a little slower than a semi auto, my purpose is for shooting paper at 1000 yards away and also maybe one day hunt, although i never have!
I hooe I was helpful and good luck with your decision, im curious to see what you go with.