Yes, in my past 3 days of using both phones, the speeds seem similar enough that I don't notice a difference. The plan prices are similar. I don't use the phone much, so I went with the 450 min plan (in both cases), which for both iPhone 3GS and HTC Incredible comes to the same $40 per month phone plus $30 per month data.
As for lack of voice and data at the same time, that's something I never use on iPhone (I don't use a headset, so when I'm on the phone, it's held to my ear).
kdarling, as a new HTC Incredible user, you may want to check out (and contribute to)
this list of tips.