The Berning ZH270. Simply because it is dependable, has auto biasing, is clear and transparent with no obvious deficiencies, is easy on tubes. Is it the best? No because that is always subject to change depending on speaker load and taste, the reason why folks often change, there is no best. I have heard other amps I really like in given systems but the Berning is just a great design that never fails to amaze me after 8+ years of owning it. I can see no reason to change it, it is too special.