Carbanion stability is determined by the s-character of the hybrid orbital bearing the negative charge.

The acetylide anion has the carbanion on an sp hybridized carbon (50% s-character), providing optimal stabilization through efficient overlap with the charged orbital.
The vinyl anion has the carbanion on an hybridized carbon (33% s-character), offering moderate stabilization.
The primary alkyl anion has the carbanion on an hybridized carbon ( -character), providing the least stabilization.
Greater s-character enables better penetration of the nucleus and enhanced stabilization of the negative charge.
Therefore, the order is .