Not usually a huge deal either way. I have Rogue Apollo with the triode/UL switch, and it still sounds like mostly the same amp in either mode. Different amps sound different by a lot - these 2 modes sound different by a little. Triode is a little smoother cleaner in the midrange. UL has a little more dynamics and slam. These amps being 250 Watts / UL (150 Triode?) and my speakers 96dB means the power loss in triode isn’t very meaningful in my case. For a long time I’ve preferred UL, but that might be changing as I age lol. Tone is the same either way - a tube roll effects more change, especially in tone.
Likewise, the 4 and 8 ohm taps both sound good, and it sounds like the same amp either way. I haven’t spent much time trying to parse out the nuances here, but I've run the Apollo amps a lot from either tap over the years. You’ll usually sacrifice some power by mismatching the tap to your speaker, and the distortion can go either higher OR lower, depending on the amp. For example, the Rogue M180 was measured by Stereophile with lower distortion (at below peak levels) from 4 ohms tap into 8 ohms, than it was from 8 ohms tap into 8 ohms. They also measured the Triode vs. UL modes, and some distortions are a little lower and others a little higher in each mode - which matches my listening. It just effects some minor trade-offs but is still the same amp.
