depending what machines you use.
for low power components such as DAC, music player, etc, 1.5 is fair neutral in sound. but if you 2.5, the sound may be too thick.
I eventually use 2.5 for subwoofer and power bar.
CAS (Win 7 64 bit / Audiolense / JRiver)
NAD M51
MC2 MC1250
Harbeth Monitor 40
Atlas Opus Coaxial, Supra Sword Cables