. . . in fact Trotsky has always been guided by the precise rules of revolutionary Marxism. Lenin is both masterful and creative in the realm of political thought and has very often formulated entirely new lines of policy which subsequently proved highly effective in achieving results. Trotsky is not remarkable for such boldness of thought: he takes revolutionary Marxism and draws from it the conclusions applicable to a given situation. He is as bold as can be in opposing liberalism and semi-socialism, but he is no innovator.
At the same time Lenin is much more of an opportunist, in the profoundest sense of the word. This may again sound odd - was not Trotsky once associated with the Mensheviks, those notorious opportunists? But the Mensheviks' opportunism was simply the political flabbiness of a petty-bourgeois party. I am not referring to this sort of opportunism; I am referring to that sense of reality which leads one now and then to alter one's tactics, to that tremendous sensitivity to the demands of the time which prompts Lenin at one moment to sharpen both edges of his sword, at another to place it in its sheath.
http://www.marxists.org/archive/lunachar/works/silhouet/trotsky.htm