Liberty has the edge for survivability on Deity. If you told me "Pick a policy tree without knowing what your start looks like. The only requirement is that you win, not that you win fast"... then I would probably pick Liberty. The extra hammers early help get archers out to protect you from a rampaging Shaka, which you would be very vulnerable to if you rushed settlers after 1 or 2 scouts... not to mention bad barbarian luck. Sure you could keep your scouts at home to escort settlers, but then they're not scouting. If you remove some of the risk-taking necessary to post competitive times on Deity, then Tradition loses a bit of an edge.
Plus, the Liberty closer is very flexible. (Great Admiral for when you're isolated on an island... for example)
Liberty is more survivable n a highly contested start when you have little-to-no good production spots near your starting settler, etc. etc.
But, if I'm going for speed? Tradition wins. On Deity. But only for speed. Perhaps it's all the time I spent warmongering on Deity with Liberty, but I feel like when you don't know what you're up against, Liberty > all. Worst comes to worst I can kill off everyone and THEN win a SV.