Magic Mamba
Newbie
Lots of great answers here and in older threads on this same topic. Here's my thoughts:
DX has great grip in all weather, especially the recent runs.
DX wears predictably, and not as fast as it sometimes is made to appear. Yes, DX starts more overstable than flight #'s suggest, but wears in and holds its sweet spot for so long.
DX allows people to cheaply - more on that below - carry lots of copies of a single mold in different levels of wear to cover a whole plethora of shots. Eagles, Rocs, and putters are the best examples of this.
Lots of popular, older molds were originally designed for DX. Hence they don't fly as well in a more premium plastics.
DX discs have more glide as compared to a more premium counterpart. There is an anecdote on here somewhere that one pro doesn't throw DX Teebirds because they are too long - he always overshoots.
DX is cheaper - two DX is one champ or star of the same disc.
I prefer DX Teebirds - cheap and easily seasoned, they hold their HSS and fly straight forever, both in distance and time. Who doesn't have room in their bag for a disc that flies straight? Rocs are also nice for this, but I love Comets more.
When wouldn't I want DX? I prefer pro-plastic putters as a good balance of softness and grip. I like my stupidly overstable discs to stay that predictably, and those are discs I don't need multiple copies of. Finally, I wouldn't want DX when I was throwing a warp-speed driver or something that wasn't designed with DX in mind. Because I don't throw anything over a speed 9 (Firebird) with any regularity, this isn't a problem. If I played in a more wooded area, I would probably prefer a star-type plastic for my fairway drivers and likely throw X Comets less (and Z Comets more).
I have a DX Teebird and it's easily my favorite disc in the bag! It flies so straight and is super consistant!