I've been Diamond now for about 7-8 years - easily making it by June(ish) of every year. This year, I'm only at 25 nights, although I probably will still make it by the end of the year.
I've moved a lot of my business to Marriott (where I am Gold), however, in many markets where I travel, Hilton has a much stronger footprint, and the prices are almost always cheaper than Marriott. For instance, for a trip next week I could stay at a Courtyard or HGI, with the Courtyard being $30 more a night.
I'm not really sure where my breaking point $ wise is for choosing one over the other, and if they are the same and my choice is Fairfield or Hampton, I'll pick Hampton every time. Some Fairfields, while they are making positive changes, and just plain AWFUL. A lot of the time it depends on the promo too - the Megabonus earlier this year with Marriott steered me much towards Marriott than Hilton.
With all that said, the bottom line is that for where I tend to travel it's hard to move 100% of my business.