Modified from an earlier answer of mine
The Bolsheviks were not really concerned so much with the efficiency of the two implements, but rather their political symbolism. In the immediate aftermath of the Bolshevik seizure of power it became painfully aware that the movement had no identifiable political symbol that was unique to the 1917 Revolution. The red flag, for example, had been a staple of various left-wing groups throughout the latter half of the nineteenth century. One of the common revolutionary songs of the period, "The Internationale" had its origins in the West. Likewise, a number of revolutionaries sung "The Worker's Marseillaise" with Russian lyrics which had been floating around in Russian labor circles since the early twentieth century. In short, in terms of political symbols, there was very little that was new in the emblems the Bolsheviks had assumed as their own in 1917. In this vacuum, various symbols had emerged either from below or from the middle ranks of the Bolsheviks. For example, the first approved symbol of the Bolsheviks was a the Red Army's badge, which consisted of a hammer and plow superimposed on a red star. When Lenin tasked Anatoly Lunacharsky, the head of Narkompros (the Commissariat of Enlightenment and Education) to hold a competition for a new national symbol in 1918, there was already a well-defined corpus of political symbols for Lunacharsky to chose from.
The design chosen by Lunacharsky was a combination of the hammer, sickle, and a short sword. These symbols were already in use in tandem or singly among various revolutionary forces, and their combination even predated 1917 such as this 1895 Chilean coin (and props to /u/International_KB for pointing this out). Lunacharsky's chief innovation was to combine each of these totems into a single coherent symbol. The hammer, sickle, and sword symbolized the troika of the workers and other class groups that brought the Bolsheviks to power: the urban proletariat (hammer), the peasantry (sickle), and the Red Army (sword). Lenin balked at the inclusion of the sword and after much debate with Lunacharsky, the sword was removed from the winning design. Lenin's rationale in the immediate aftermath of Brest-Litovsk and the Bolshevik's promise of "Bread and Peace," was that the sword "is not our emblem and does not represent our policy." The emblem became ubiquitous in what would become the USSR and was prominently featured on the cover of the first constitution of the RSFSR in November 1918.
The choice of the sickle and hammer was one which simultaneously tapped into both a long tradition of political symbolism and sent a bold message about the Revolution. The hammer had been a symbol of the working classes in Europe for quite some time, and the sickle was also a symbol of the Russian peasantry. As hand tools used by individuals of a distinct class background, both images together conveyed a message of class solidarity of the toiling masses against their oppressors. This was not just an idle symbol in the context of 1917/1918; the Bolsheviks portrayed themselves both to their enemies/rivals on the left (Mensheviks and SRs) and to domestic audiences that they were the true champions of both groups.
Sources
Acton, Edward, V. I︠. Cherni︠a︡ev, and William G. Rosenberg. Critical Companion to the Russian Revolution, 1914-1921. Bloomington: Indiana University Press, 1997.
Stites, Richard. Revolutionary Dreams: Utopian Vision and Experimental Life in the Russian Revolution. New York: Oxford University Press, 1989.
Stites, Richard, and David M. Goldfrank. Passion and Perception: Essays on Russian Culture. Washington, DC: New Academia Pub, 2010.
