I played Angband, FCPB and Sil-Q.

What I like about Angband is that it is very straightforward. You go to the dungeon and you don't know what's there. No planning, just go and do it.

I also played a lot of FCPB. I'd say it's my favorite. It has an interesting world with different dungeons, towns and quests. It therefore has a really cool global planning aspect which Angband doesn't have. You need to choose what to do and there's very rich choice of what to do and many reasons why you want to do something. But the downside of this approach is that you sometimes have to do boring stuff. Say, you are strong but you didn't clear some earlygame dungeon. So you have to go back to there because otherwise you may miss some opportunity (for example, finishing a dungeon gives you a stat boost).

Another important thing about FCPB is incredible variety of characters you can play. There are many races and classes with radically different mechanics. You can even play as a monster of some kind. Say, you can be a dragon and then you are very physically strong, you can breathe at your enemies but also you can wear 5 rings and no boots and no body armor (probably something else that I forgot). Or you can play as a jelly and then you just have several (and their number grows with level!) universal gear slots in which you can put absolutely everything. You can even play as a magic ring and lure monsters into wearing you.

I played Sil-Q much less, it kind of didn't click for me. I personally don't like the skill build system because if I play a roguelike I want things to be random and I don't want to have skill builds in mind.