OP here.
In my opinion, I recommend using Xcode 4. It's what I'm using and I'm glad to be learning current content. Kochan's Objective-C book (the one I link at the beginning) works fine with Xcode 4, until the end of the book where it delves into Xcode 3, but I haven't even made it that far. Most of it is raw Objective-C so it will work fine.
Kochan is a great guy (he personally responded to me on his forum) but I found the book a bit too advanced (and a bit too slow) for my tastes. That said, I definitely plan on reading it cover to cover when the next edition comes out. I feel like it wasn't the best to get me started but feel it's a great intermediate level book once I'm on my feet.
I will recommend two resources for you that have been very helpful to me, best of all they're free:
iPhone iOS 4 Development Essentials Xcode 4 Edition
Objective-C 2.0 Essentials
The first one is completely updated for Xcode 4. I don't know whether it's the best or not but it's been helping me and it's free. It covers the very BASICS of Objective-C but gets you making an iPhone app immediately and it feels good learning Xcode/actually making progress and making things work.
The second link is by the same people and is their book on Objective-C that goes more in-depth but still jumps from issue-to-issue faster than other books, but somehow I actually felt like I was learning more from them than other in-depth resources. They explained things really well and answered questions that other books left me hanging on. And maybe I have ADD (not really that I'm aware of) but I like jumping from thing to thing quickly, feeling like I'm making progress. Of course I actually want to learn the content too, but I feel it gives you a nice medium between knowledge and speed.
These two books are much shorter than most at about 200 pages each so I'm sure afterwards you'll need to move-on to more in-depth content but this is giving me the jumpstart I needed making me feel like I'm making progress and past the initial hump of being super confused. Note there are a decent number of grammatical mistakes, and in a few places I noticed them accidentally use C# code instead of Objective-C (in very minor places, like for putting text he accidentally used Console.WriteLine instead of NSLog) but I haven't found any of it actually impede my learning process.
I bought the .PDF versions of both for $13 each but they contain the exact same content, I just prefer .PDFs.
Hope this helped, let me know if you have any questions, I don't check here a ton but I'll try and keep my eye on this thread. And I'm sure as I learn more I'll become more active.
My goal is to have a VERY simple app (free of course) on the app store within a month or so...