Photoshop CS5. I have all photoshop applications from CS.
I still prefer the use of CS2 & CS3.
Cs4 & 5 are no different, a few added extras nothing i would use anymore now i've subsided from being a designer, to just a casual artist.
Also CS3 & 2 both run a lot quicker, and their portable versions are also great.
Preferably your Design set up should be designing between Illustrator & Photoshop. Illustrator is perfect for line art & vector work, where as photoshop is great for the added effects and the final design stages.
Content-aware fill, very useful tool, for photo manipulation, I use it all the time. I got CS5.
I've got CS4, but I have to agree that that tool would be extremely useful while manipulating images. Would save lots of time and looks much more effective then other methods such as the patch tool which don't always come out looking right. CS4 actually came with the first content-aware option that I'm aware of called content-aware scaling. I didn't think they would come out with so many more content-aware tools, but these would all make things much easier.
Also CS3 & 2 both run a lot quicker, and their portable versions are also great.
No portable versions are legitimate keep in mind as Adobe apparently doesn't do that, but there are already portable versions for both CS4 and CS5, and of course if you have a good enough computer the speed won't matter too much if you can do more with it.
