Hero for sure.
I have the G1, and android is a beast of a mobile OS. Blows away iPhone software and WM6.5, IMO. The app store is definitely better than the pre, and consider this: By then end of 2009, every US carrier will have at least 2 Android handsets. By Q2 2010, probably 5-10 per carrier, judging by the leaked roadmaps from carriers. How will any other app store compete with that kind of market penetration?
Android 1.0 software was released in maybe December, 'Cupcake' 1.5 rolled out nationwide to G1s in June/July [added multitouch, on screen keyboard, maps updates and more], and 'Donut' (they're not calling it 2.0, but still a major upgrade) is due by Christmas. Steady upgrades and ongoing, innovative development are just a few benefits of an 'open platform' supported by a huge community and Big G. And, if you want to upgrade to Donut right now, you can [with the proper know-how]. Google loves developers, Palm tries to shut them out.
Literally my only complaint about the G1 is the shitty case, and the Hero addresses that with a slick teflon plastic coating that doesn't scratch or pick up dirt.