Oppose Woolwich attack is clearly the WP:COMMONAME for this incident. In addition, any reader who wouldn't recognise '2013 Woolwich attack' as referring to this incident, is clearly not going to know that 'Death/Murder of Lee Rigby' refers to it either, so it offers no advantage on that score. Quite the opposite infact - to the uninitiated, 'Death/Murder of Lee Rigby' could refer to any number of incidents/motives/places, whereas most reasonable people would assume '2013 Woolwich attack' refers to some kind of attack in a place called Woolwich that occurred in 2013, which is good enough as a starting point. I don't recognise any of the other articles listed above as being about this sort of incident, so it's hard to put any weight on that argument at all.