IMHO if you're comparing with the 3 choices above, the Desire is the clear choice. Legend is an old gadget that might not even get FroYo unless you root, so skip it. With iPhone 4 around the corner, the 3GS is a very bad choice. So if your options are the 3 above, go for the Desire. If you want to wait for iPhone 4, then its a good challenge between the 2 phones. However, as for me, after 3 weeks of intense research, I've chosen the Desire over iPhone 4, and I've never regret that move 1 bit, this phone is FANTASTIC!

I'm not biased to any phone, I'm just telling you which is the better one. After being a user of the iPod Touch 2G, the annoyance of the Apple series is still there. Yeah sure multitasking is finally in but man that annoying as hell syncing still proves to be a mega hassle!!! No bluetooth except for headset, no nothing! And many more.

Anyway finally, if terms of ease of use, the iPhone 4 will be friendlier, if you like to drive your phone to meet various needs, to be able to explore further on what the phone can do for you, go for the Desire.

Hope this helps