I'm not sure about the antenna issues, that one might be worth waiting for if you live in an area where your carriers service is not that good. My carrier works really well here and I have seen no difference between my 3gs and my 4, so I can't comment on that.
Regarding the screen issue, I wouldn't consider that something to hold you back. You have a higher chance of getting one without an issue then you do with one that does have an issue. If you do get one with a messed up screen, just get it replaced for free.