Let's say I have a couple spare BTC to invest, why should I bet my money on DRK above XMR at this point in time? XMR hasn't failed me so far in my predictions, but when I look at DRK future wise, it seems to blurry to me.
XMR will have uptake issues because it isn't descended from Bitcoin. Not insurmountable. But it will take time and a considerable effort.
Whereas DRK after RC4 is good to go. And ready for further enhancements. I have at various times had some of the other anon coins. But I won't go into why I've got rid of most.
Instead I'd say dark is more transparent about what they are doing than the majority of other bitcoin-based anon coins
You can see progress on rc4 on darkcointalk.
Pretty much all of the rest have "anon soon promise!" and really fuzzy descriptions on how it works.
Drk has learned and adopted and gotten stronger, better more professional.
The whitepaper is detailed on how the anon works and is being reviewed by an expert (kristov atlas)
So we are past the hype stage and onto delivery.
*Edit - and that's why I vote DRK