On my tube amps, I've always gotten the most noticeable changes rolling the input gain tubes. Power tubes basically boost whatever is fed to them, but they do have their own voice as well and can also bring some change, most usually in the lower range and sometimes in midrange warmth.
In the long run, it's more economical to stick to rolling the small tubes. My rolling MO is to find a power tube I like that is readily available since they consume themselves at a more rapid pace. Current manufacture Tung-Sol's are my go to choice in that regard I do the same with the small tubes, my reasoning being that I would hate to fall in love with a rare NOS tube and then have to switch to something else because it was too hard or impossible to get future replacements. The best NOS small tubes never get cheaper because there are less of them available as each year passes. The up side is that, depending on how they are driven, they can last upwards of 10,000 hours.
Tube rolling is fun, but it can also be an expensive pain in the keister. A tube amp that offers switching between triode and ultra-linear gives you an additional choice for sound treatment with the same tubes, and IMO, it's a must have.
