In terms of fan support, Memphis.
In terms of sheer "meh"ness, Toronto.
Toronto's always been a really good city in terms of fan support. You don't really blame the folks for "meh-ness" after the team they've had to root for these past couple years, but it's definitely a good city for the NBA.
Memphis, though. Ugh. Contract them, we'll lose one of the league's worst owners and worst GMs. They'll be about eight people, total, who'll be p---ed off and four of those are in Chris Wallace's family. It's not a big market, it's a great market for college hoops but with seemingly little desire to embrace the NBA product. That's the most glaring example if the league ever DOES contract, or wants to put a team in Vegas.
Atlanta has historically been a pretty good NBA town, back in the day, but they don't seem to embrace the current team even when they've played pretty good ball. It's still a city that's proven it can support an NBA franchise.