I think that only time will tell on this question. Right now, the availability of P-25 equipment on eBay is why that standard seems to be out there more, but the equipment is still pretty expensive. Icom's D-Star is coming along, but hasn't reached a wider acceptance - yet. I have seen and heard about several P-25 repeaters out there on the amateur radio bands, but I haven't seen or heard about too many D-Star systems - yet.
We'll see......