I've had both in FRN. I miss the D-fly more, only because as has been pointed out, there's Spydies with better BTH ratios than the Delica, and I have a couple of those, LOL.
If you plan on using this knife at the office, the D-fly would definitely be more NKP-friendly. In G10, you will have a knife rarely seen, with some 'presense' in your pocket. The FRN is so light, you can hardly feel it. I also strongly prefer the wire clip on the 'Fly, to that of the Delica.
If you plan on using this thing for more 'outdoorsy' activites, or even as a back-up in the kitchen, then the Delica would be the choice. You simply have more edge there. It can also fit into a self-defense role, if you were pressed. The FFG is certainly the right one to pick, IMHO.