There were six leaders between the time period 1855-1064 and to determine who was the most successful we have to know how to measure successfulness. Successfulness is measured over a range of things such as achieving aims, economy, war and the public opinion and opposition to the leader in power.
Firstly war was a crucial part of the time period 1855-1964 with Russia going though small wars to huge full blown World Wars. Stalin was clearly to most successful leader in terms of war as he won WWII with shear mass of soldiers and equipment like tanks. Stalin won with quantity rather than quality however came out of the war the victor and a hero to many Russians. Stalin led Russia into the Cold War against America and managed to take control of much of Eastern Europe using East Germany an 'iron curtain' like Winston Churchill famously said. Khrushchev and Lenin wasn’t that unsuccessful either although Lenin did make Russia leave WWI he managed to perform a coup and get into power. Khrushchev received a bit of an unrest from attacking Stalin however it was soon interrupted and over. Alexander III was careful and generally stayed out of wars meaning he didn’t lose any however he did win one in 1887 against Turkey although he won he gained very little due to great powers intervening. Alexander II also tended to keep out of wars also however when he came into power he was half way through the Crimean War which had 500,00 casualties. The Russian soldiers only had 1 rifle between 2 and most of them were peasants. However what makes Alexander II more credible is that he improved the training of troops after the war and didn’t enter Russia into any wars himself. The most unsuccessful leader to do with war is hands down Nicholas II who in 1904 enter Russia into the Russo-Japanese war and lost with the Russian navy nearly being completely wiped out. Further more in 1905 Nicholas II was very close to losing power