I've certainly mentioned in the past that the 3130 is a great amp and the 3020. I've not heard a 3150 to be honest so can't comment on that particular amp - never even seen one before. Can you try it before you buy? If it's in good condition and the sound appeals then you could save yourself a lot of money buying the cheaper amp. The C352 is a great amp but different to the older ones. If you plan on playing loud I'd go for that as the dynamics and speaker driving power will be spot-on. For quiet to moderate listening levels I don't think you can beat the older Nads - providing they are still serviceable.