There is some good discussion/information in these posts/existing topics:
Output transformerless vs transformer coupled
Single ended vs push pull vs ultralinear
Triodes vs pentodes vs beam tetrodes vs directly heated tubes
Tube rectified vs solid state rectified
Use of feedback
9-pin vs 8-pin vs 4-pin base tubes
New old stock vs new production vs re-issued tubes
Headphone only amps vs speaker amp capability vs preamp capability
Output impedance and power output matching
General sound signatures for various tube types, tube manufacturers (which can be different from the brand/label), tube manufacturer’s country of origin