I chose other because I don't have one set answer....not that I've done a ton of upgrading (see my post in the 'previous phones' thread compared to most haha), but I basically decide on the phone I want and then find (or wait a bit, as the case may be) for at least a price I'm willing to pay, or otherwise the cheapest place/method i can get it. For the Epic 4G, I waited until someone had it for ~$100 or less...Amazon Wireless was the first to drop to that price point and I jumped on it. With the Photon Q, early on it was discovered that at least at some Sams Clubs, you could obtain the phone for just under $75. The closest one to me that carried it (or Sprint phones in general) was in Nashville an hour away, so I didn't immediately jump on that even then, but coincidental circumstance brought me to Nashville to work over a weekend, and I took the opportunity to upgrade then finally.
I guess the best overall answer would probably be to say 'not directly through Sprint' thus far, mainly because that has tended to be the most expensive route for the phone I desired. I pretty much approach this like everything else I buy: Once I make a decision on specifically/exactly what product I want quality wise, then I do as much research as possible to find the cheapest place I can get it (barring any obvious red flags review-wise on the company that sells it).