In order to secure the presidency: Biden
In terms of long-term political success: A narrow loss in 2016 is probably the best outcome for Democrats if we look at what this means for the 2018/2020 congressional/gubernatorial elections. If we had a Democratic president right now, the Democrats' would likely have no chance at a majority in either chamber or improving their very weak position in state legislatures, and the incumbent president would probably have an uphill fight in 2020 after 12 years of a Democratic president. Because Trump won in 2016, the Democrats are probably favored to win the House and several governorships this year, the 2020 Senate map is very promising as well, and I would argue that Trump is likely going to lose reelection. I think the Democrats are well poised to control both chambers and the presidency during the 2021-2023 period, and hopefully they could capitalize on it as well as they did in 2009-2011.
I agree 100%.