The "problem" with the iPhone 4 was a bit overblown, and really it's more accurately called a design tradeoff. It could pick up and keep a signal in weak areas where no other phone could. But the signal was attenuated rather easily if you put your hand in just the right spot, and make it drop completely in areas with, say, 2 or fewer bars. A case made this a non-issue. Yes, you can make any phone drop the signal if held just right, but it was never that easy on my 3GS, and I doubt quite that easy on most any other phone out there.
That said, I've recently upgraded to the 4S, and there's no question that the weak spot has been eliminated. I can still quite easily make my wife's iPhone 4 drop the signal at home, but on the 4S… I have to struggle to get it to drop even a bar. The Verizon iPhone 4 already had a redesigned antenna, similar to the iPhone 4S, but from what I've read, the 4S improves on that still some more.
Oh yes, if you are buying now, the right call is to get the iPhone 4S. Siri is not a gimmick by any means. I now dictate all my text messages to my wife, which has made my life loads easier. Actually I dictate most everything now, depending on where I am. Besides, that 8GB iPhone 4 will run out of space REAL fast.