It's a combo for me as well.
I actually find heroin quite stimulating, with a mix of nods that set in for a bit during some point of the effects.\
And by "stimulating", I'm not talking about the effects one would think of from stimulant drugs.
It's more of just a sudden desire to want to be more productive, while also not having physical pain & depression holding me back from being able to get whatever it is done. It feels very natural, where as stimulant/amphetamine stimulation feels forced & edgy.
It also depends on the opioid & my tolerance for me. For example, in the beginning, buprenorphine was quite stimulating & even made me chatty, but after years of being on it, I actually find bupe way more "heavy" feeling than heroin even.
When I use heroin, I get a clear mind, energy, motivation to get shit done, feel content & peaceful. I almost can't even tell that I'm "high", it's just this natural feeling of being pain-free & in a super good mood.
But when I take bupe, I feel tired, heavy, lethargic, bored, flat, etc..
So there's so many variables at play here. It's typically stated that thebaine derivatives are more stimulating (i.e. - oxy, hydro, bupe)... But I've never seen any evidence or science backing up why they would be more stimulating, other than the fact that thebaine is a convulsant.
So in the end, most opioids are a mix of both stimulating & sedating for me, but some are a lot "heavier" feeling than others. And i'm sure personal bio-chemistry has a hand in it as well.