There is no such thing of which hotel program gives the most UA miles per dollar spent, as each program doesn't give miles equally to all of their brands, e.g. Doubletree give 500 miles per stay vs 100 miles at Hampton Inn even both are in the same chain. It also depends if you usually have 1 night stay or multiple nights stay, so you would choose variable miles instead of fixed miles, e.g. if you have one night stay at Hilton price at $299, of course you would choose fixed mile option as you would get 500 miles instead of 299 miles.

And sometimes if they have a double mile promotion, of course you would do multiple one night stay on fix miles with all different hotels instead of variable miles just in one brand in order to maximize the miles you earn, e.g. you get 3000 miles on fixed miles option if you stay at 3 different Hilton Garden Inn instead of 3 nights in 1 Hilton Garden Inn for $150 a night on variable miles would only get you 450 miles.

My advice is don't stick to one program and find the cheapest rates (booked thru the chain directly instead of 3rd party especially name your own price site like priceline and hotwire, as they can deny you from earning miles) unless you want to earn hotel status.