Any holiday weekend is very hard for me to get time off. While I have ten years of senority, in my current assignment I am (thanks to 100 layoffs) one of the junior guys. This means getting vacation on or around a holiday is next to impossible. Same thing for my wife.
Also holidays tend to be higher rates and less flexibility on reservations due to demand. I would also expect more traffic on the trails.
Mid to late July or early August would take my vote.
Northern Colorado, Georgetown as El Cid put forward, would be some closer and offer different opportunities for side trips. Both plusses in my book.