IMO among these roguelikes Angband is the only one that can be safely played unspoiled.
There is A LOT of hidden and not-so-easy-to-figure-out-on-your-own content in ADOM.
But I guess it can be won unspoiled after many attempts.
After all it's not that hard when you get used to it.
There are A LOT of things that have SIGNIFICANT impact on your ability to win in DCSS.
There are A LOT of hidden and completely undocumented mechanics.
If you have natural affinity to math and statistics, probably you can figure it out on your own.
But I sourcedived a lot to understand WHY THE HELL MY TROLL CAN'T HIT THINGS!
I had to do some not-so-obvious choices after calculating hidden parameters.
Developers claim that there are people who ascend unspoiled.
Well. I can even believe this. Because in DCSS you rely A LOT on MIGHTY GOD RNG!
Basically by trying and trying and trying (and dying and dying and dying) you can
finally get character with some awesome near-starting equipment who is more or less safe from
so-loved-by-DCSS sudden death. Why so much about dcss?
It's freaking addictive
I have quite contradictory love-hate feeling toward DCSS.
And there is big difference between simple ascension and all runes ascension
Can't actually say much about Nethack, since I never ascended there.
But from what I read from various posts about it, there are a lot
things that almost require spoilers.
RLs to consider:
FrozenDepth
IVAN
DoomRL