The 3GS felt really good in the hand. Ergonomically it worked better for me. The iPhone 4, in my opinion, looks much cooler, but doesn't fit as nicely in the hand.
Yes, the 'soapbar' design of the earlier iPhones fit your hand much nicer. While not exactly painful, the iPhone 4 edgyness actually hurts your hand a little. Also, it's way more slippery. And how much better the antenna design may be, I can get it to disconnect from my Airport Extreme 6 meters and a chalkboard-wood-and-rockwool wall away; just by holding it in a comfortable 'landscape' grip over the top of the iPhone.