While I can't confirm that there's actually a difference, I believe there might be. Sites such as Andronica claim that there is definitely no difference between Heros tha have the "with Google" branding on them and Heros that don't. (
Is your Sprint HTC Hero sporting the ?with Google? branding? | Google Android Blog)
I can tell you that my first Hero that didn't have the "with Google" branding on the back had static/fuzziness coming from the earpiece and I felt that battery cover came off to easily with barely a touch. When I went to a Sprint store to exchange the phone I wound up with a new Hero that had the "with Google" branding on the back. I didn't request it or anything (don't think I could've anyway).
Here's what I noticed right away about the Hero with the "with Google" branding on the back besides the earpiece working correctly: the battery cover fit snugly and also seems to give a better grip because it seems like it has some sort of coating that's feels kind of like rubber. Granted I can't remember for sure if my original phone that didn't have the branding had the same coating on the battery cover but I definitely noticed on the one with the branding. My phone also says Rev A, however, according to an article from AndroidCentral this doesn't matter and is just a visual display bug. (
http://www.androidcentral.com/does-your-sprint-htc-hero-have-google-logo).
What I'm wondering is this: Is Htc testing out two different manufacturers and using the branding to see which manufacturer is better? I know that sounds like a conspiracy theory and I have no information to back it up but it does make me wonder.
I do want to note however that I'm not trying to say that all Heros that don't have the "with Google" branding are defective. I'm sure there are many that are working just perfectly. This was just my experience.
Good luck with your decision.