From a viewing standpoint, I loved Rio. Very picturesque and beautiful. The best cities are the ones with the infrastructure & economic stability already in place (Los Angeles, London, Tokyo, Sydney).
Out of the cities that haven’t hosted, I would love to see an African nation host. Also, Toronto & New York would be cool.
Selfishly, I would love to have the games in Detroit. We should of had it in 1968, but Mexico City just beat us out. We haven’t had the economy to host them since the 1968 riots & 2007-08 stock market crash. I am hopeful for the future though (maybe a combined Detroit/Windsor bid)