ASCII = 256 characters, not all of which are even used
Graphics set = all the ASCII tiles, plus individual tiles for each dwarf profession, creature, and other race in the game, i.e. a lot more information conveyed.
I can play either way, but Mayday's tileset is what I "grew up" on while learning DF, so that's what I revert to whenever I need to get away from ASCII or another graphics set. ASCII just hurts my eyes after too long. After a while you feel like you're trying to read the fucking Matrix code, and in the meantime 94 goblins just popped by to say hello and you can't find the goddamn catapults because it's in ASCII, FUCKING ASCII.
ASCII was originally used for gaming out of necessity, not by choice. Just because it came first doesn't mean it's better. There's a REASON why most of humanity no longer lives as nomads eating roots and berries and shitting in the middle of a field while watching for pissed-off wild boars. Progress is cool. Try it. If you're honestly going to argue that codepage 437 is better, then you must be replying to this thread from a BBS program and running MS-DOS 5.0, because 6.1 is "just too newbish". Otherwise, you're a hypocrite. So a 16x16 PNG tile doesn't look like a turkey... so what? Neither does a fucking "t".
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So, how 'bout them U.S. elections? In my state we're putting through an initiative to legalize marijuana. It's pretty awesome.