If I had to pick a top 3 (in no specific order):
Rogue
Infra Arcana
Frozen Depths
Top 5, add:
Hydra Slayer
Nethack
For me, among ascii roguelikes those would be DoomRL, DemonHunt & Frozen Depths - to a large extent because most of the others I tried have such a cumbersome interface I couldn't really be bothered playing them for long.
DemonHunt in particular I've been playing quite a bit in the past week.
I would also put crawl pretty high up there, I can sometimes muster enough will power to play it but haven't in a long time.
I tried playing angband, nethack & adom many times (as well as rogue and larn) but never managed to get into them - the curve is just too steep & life's too short.
I also think that having sounds (and to a much lesser extent music) makes a huge impact, even if they are just blippy 8-bit/PC speaker type sounds- it just feels so dry and unengaging to not have any auditory feedback (funnily enough this bothers me a lot more than ascii graphics).
In the past little while I've been playing around with coding c to the bare metal on dos (thanks to dosbox, open watcom 16-bit c compiler & raw access to CGA memory space).
Other than the obvious challenge, I was really surprised how little hindrance targeting the original IBM PC with CGA's default text mode (640x200 pixels, 80x25 chars, 16 colors) was and how much the traditional roguelike interface (as seen in nethack, rogue, angband, et al) is
not the result of shitty old hardware (well, maybe it is but it's not the result of shitty PC hardware).