Of course everyone is going to have a different opinion due to different reasons and variables.
I like the answer slice gave. Test is underrated.
But I would have to say winstrol. Nobody ever really mentions how strong it really is but for me it is extremely effective
Man I feel like I'm parroting because I agree completely on both. I think the OP mis-worded the title. I think he's asking what compounds we underestimate/underrate, not the ones we value highly, that are often underrated in general.
If that's the case, I always underrate test. I always use it but it is literally the last compound I think about in a cycle since I've typically ran it low and let the other compound do their part.
When I tried running it higher, I forgot awesome it is at doing everything that other compounds are known to do. I realized I need to keep my diet, estrogen and other factors on point, but it can build muscle, give amazing fullness, burn fat, and just feel great.
The compound that is often underrated that I've grown to love is like you said, winstrol. Never get achey joints, gain a lot of strength and get a very grainy look when I'm under 8% that is noticeably different than what I can get off just masteron and tren.