I cant make that decision for ya, but I can tell ya a few facts about my Z:
1 - First off, its a 6MT performance.
2 - I live in Queens, NYC
3 - I hit a lot of traffic, and I have a second car for rainy/snowy weather (which is automatic also)
4 - But, I've noticed so far that I can drive stick fine in traffic while sipping coffee, talking on my cell, or holding my girl's hand (I make her row the pattern, my hand on top of hers)
So, in conclusion, stick is very livable. Its not a pain in the ass once ya get used to the super touchy clutch a new Z will have. In my opinion, the 350z's gearbox has got to be up there with porsche MT's and the like, it has been described as "notchy" by many journalists, but I prefer the term "crisp". There is no slop what-so-ever. There are no energy absorbing bushings. Your right hand feels as it is directly connected to the transmission. If I were to make the decision again, I'd choose the 6MT..... twice.