For most folks, a 12/2+G or 10/2+G run from the 'quiet' side of the panel is perfectly adequate. If you have big power hungry monoblocks, then a 10/3+G providing 2 circuits is still more than adequate.
In an existing house you may not have panel space or the luxury of picking a 'quiet' side of the panel and electricians rarely leave service loops adequate to rework loads by re-homing breakers. In that case an solation transformer although hugely expensive may be worth it to you. For most, good power conditioner will have to do.
In any event, a digital oscilloscope, preferably with spectrum analyzer capabilities is really the only way to see how clean or dirty your power actually is.