Ethene is the most reactive hydrocarbon among these. The reason is that it is unsaturated, hence, more reactive than alkanes. On the other hand, ethyne (despite being unsaturated) has a very short C?C bond length $ (1.20\cdot \overset{\text{o}}{\mathop{\text{A}}}\,) $ ) due to which bond becomes stronger and hence, it is less stable than ethene.