I wouldn't wish the curse of the Olympics on any city I've lived in and have significant ties to, so that rules out both Dallas and Washington, for me.
Seriously, hosting the Olympics is one of the worst curses a city can bring on itself.
Modern-day, maybe, but Melbourne was a huge winner for hosting 1956. Not only did it remind the world that we existed, it set up a great legacy for Melbourne in terms of both sporting infrastructure and sporting heritage. Without the Olympics, we wouldn't have our sports precinct, which is possibly better than any other in the world, and is right in the heart of town.
Sydney has gone to the dogs post-Olympics, and it would be fair to suggest that part of the reason is a shift in priorities in terms of infrastructure spending that occured due to hosting the games, but more realistically comes down to poor governance more broadly. I'd still suggest it was an absolute positive for Australia as a nation, and probably a positive for Sydney itself.
A city like Istanbul would have a similar experience to Sydney's, I'd suggest. Already known, but boosts its profile, massively boosts the profile of the nation beyond Istanbul, and if well-managed, leaves a strong legacy for the future in sporting infrastructure. Their olympic stadium is already built and functioning well, so you'd add 30,000 temporary seats and be good to go, along with increasing the transport and safety infrastructure, which would be no bad thing for a city that aims to be one of those top-tier cities that it was in the past.