I feel like pentode has a little faster, or harder, or more immediate attack. I notice more definition on the front end of the note.
Tridode can be softer, probably what I would describe as a bluesier feel both clean and with distortion.
Both good, go with what you like.
Each will take different preamp settings for optimal enjoyment though. So just switching back and forth may get you a general idea of some of the characteristics of each, playing around with the treble, and volume of each channel will show you how they react differently. Just an example of this, hitting triode with the treble around 8-9 on Rhy1 and turning the volume up on that channel will get you a little grind with the clean. Pick the note harder and you'll notice this more, back off and there won't be as much.