Had Walton made it another 3 or 4 years with health in Portland, he would have been the obvious choice.
Clyde may well be a better overall player than Dame, but I think these questions also involve a touch of off-court meaning and importance as well. And no Blazer ever has embodied the team and represented the franchise as its persona and face like Lillard.
That quality in conjunction with his career-long performance gives the edge to Dame for me.