in your opinion am I better using this on a warrior, shaman, or paladin?
Congrats!
If I understand the proc mechanic correctly (and I've never had the pleasure of owning one, just talking to people) then its a chance "on event" to proc... events being attacks and even its own proc can proc it. This (in my opinion) makes ret a poor choice. Fewer events that will proc the wound means fewer procs. The flip side of this is that the proc can serve to fill in the "gaps" on a ret's... lets call it "slow" rotation and make their already scary burst even scarier.
Shaman become the funny choice here. Windfury gives you lots of events every time it procs and those events can proc lots of procs and you can *potentially* but very rarely just... delete a twink with it. POD shaman kinda live and die by the proc though and to be fair, the scariest shaman I've run into are spec'd Nova or run a more spellhance build. Not to say it cant work, but I feel like a POD on a shaman goes in its tool kit, rather than being the main show... if that makes sense?
Warrior has a consistent string of reliable events that can proc POD and I think (though, being a 39 warrior myself, I might be biased) that this is your best choice of class for the POD. Granted, you're gonna spend a lot of time in sword/board and not swinging it but when you do get to slap on a 2hander and do work, I think warrior makes the best use of it. Big bleeds, consistent overpower ever 5 seconds, sweeping strikes... you're gonna hurt.
All that said, this is WOTLK 2, Electric Boogaloo. Play what seems fun and exciting to you. And know that not having a POD doesnt break those other classes. It's also not gonna make those classes. The heirloom axe is really quite good and outside the proc, stands its ground with the POD. After accounting for the AP from str, its worth 7 less top end dmg but comes with like 1.4% more crit and 190 more health. So if you wanna play these other classes, dont feel like you cant without a POD. I do just fine swinging my heirloom axe on my warrior.