Are we talking about young stalin, middle stalin or late stalin? Its important.
Early Stalin before October 1917 was on the right of the Party. Lenin was more, um, opportunist, in his ideology. Though over the issue of Party, Liquidationalism, Internationalism and Revolutionism Lenin and Stalin had different positions. Most notably Lenin went Stalin's throat over Stalin's handling of Petrograd, and Stalin's anti-revolutionism in 1917. (Significantly, Lenin welcomed Trostky's revolutionist faction to the Bolshevik party at this period).
During the Civil War Stalin followed party line.
Immediately after Lenin's death, Stalin's line retained a right position against Trotsky, then a left position against his rightist allies.. then continued flip flopping until his death. Stalin's political arguments were primarily centred around power to the General Secretary, and the organs under his influence. Lenin's political arguments had always been about revolution in Russia and the World. So we can compare Stalin and Lenin's opportunism on the basis of their goals.
In his late period, 1933 onwards, Lenin was merely a figure head to legitimise Soviet society. When inconvienient, the opportunist shed Lenin and took up Great Russian Nationalism or even the orthodox church.
(While this article may sound sympathetic to Lenin, I also revile Lenin for his corruption of the Soviets).