I’ve recently become interested in guitar amps that use a pentode input stage. Compared to a triode, such as a 12AX7, a pentode usually will have much more gain but the drawback is they can be noisy.
What I’v noticed is the pentodes seem to lend themselves to playing full guitar chords. Where an overdriven 12AX7 seem to work well with 5ths, a pentode handles more complex chords better to my ear. I believe it has to do with the even order harmonics that pentodes produce so well.
Here is a demo of an AC15 that has a nice comparison of the EF86 pentode channel and the top boost channel that uses more traditional 12AX7s.