ASCII, for two main reasons:
ASCII tends to provoke my fantasy much more then tiles do, although they're very nice to look at. And I'm also too idle to learn monsters' tiles, when I already know their glyphs.
Second reason is, of course, online play. Not only does it allow me to watch other people's games, especially in interesting locations. But it also allows other people to watch my game and comment my play (both in a helpful and snidy manner, when called for).
For one, I have one SpVM all-runer, which I would probably not get without great advice by Casmith789 and Monky during my Pan times (thank you, guys, yet again
).
And of course, the bragging is so much easier with the ##crawl channel and their bots
.
... and forgive us our YASDs,
As we forgive our developers,
And lead us not into the Abyss,
But deliver us from Sigmund,
For Thine is the Roguelike,
the Orb and the Victory,
now and forever.