Speaking as someone who had no difficulty adjusting to the default Dwarf Fortress CP437 set (since I came into this game off of Nethack), I have to echo the personal-preference sentiment. My personal preference, based on familiarity, is the default set (although these days I use the excellent
Hanuman square curses set. I have to say this is dependent on several factors.
First of all, I think that due to the presence of less immediately visual data, the curses tileset encourages a more cautious style of gameplay. I enjoy this more cautious playstyle. Someone else might enjoy making split-second decisions based on visual data without pausing (or at least without pausing for long); I enjoy pausing and confirming the identity of all participants in each event that requires my attention before making any decisions.
Second of all, I find most graphical tilesets to be too crowded. Graphical tiles simply have too much going on in each space for me to interpret them at a glance. To borrow an example from the New York Times interview of Toady, I actually have an easier time deciphering "♠§dg" (a dog chained to a tree, about to be mauled by a goblin) than I would of a tiny lineup of graphical symbols for tree, chain, dog, goblin. This is in the context of the game, mind you, where I'd have been watching the approach of the goblin and seeing the symbols (graphical or curses) flash. If the tiles were larger and the movement was more fluid (rather than warping from tile to tile) this wouldn't be the case, but, well, there you go.
And finally, my thoughts on curses vs. graphics in general. When it comes down to it, both the curses set and the graphical sets are displaying purely symbolic representations. The curses tileset is impressive for the amount of data it manages to convey with so few symbols at its disposal, and the graphical sets are impressive for the amount of differentiation they manage to cram into such tiny spaces. At the end of the day, though, a miniature picture of a human and an uppercase "U" both do the
exact same job. The one purely functional advantage that graphical tilesets have over curses (removal of ambiguity, since that "U" might be a unicorn) is not really that much of an issue for anyone who's well versed in the game, since humans have very obviously different behavior from unicorns attached to them. Now, if there were a graphical set that somehow interpreted the state of each creature (changing their symbols based on, for example, how many limbs they had or what they were carrying), that would be a step towards a truly "graphical" (rather than symbolic) display.
...now, once full tile support is implemented, I'll be the first to scrape together a tileset based on multiple font faces for different types of map features & creature classes.
Never giving up codepage 437 in DF. Never.
+1. Different typefaces and perhaps glyphs from different alphabets would go a long way towards removing the ambiguity from curses.