Warning: Personal opinions lie ahead, and y'all know how opinions are... I apologize in advance for any of this that turns into an early-morning pre-coffee geekrant. :3
I like objc. I think it's a good OO extension to C that lacks the mess of certain other C-derived OO languages.
I think if you want massive portability, it's not the best choice, though. Yes, it will compile on many platforms, but you're going to end up linking with a bunch of native C libraries on each platform for cross-platform graphics, sound, etc, and having to not only manually manage the heap allocation associated with those libraries, but also manage the differing build process on all the platforms you want to support.
(Here's that pre-coffee geekrant.
) My opinion is: it's almost 2012, not 1980. Automatic garbage collection is a wonderful thing, despite what some might say. ;P The only reason to be managing your own heap allocation these days is if you're doing teeth-on-the-hardware OS-level stuff or targeting tiny embedded systems that don't have room for a rich execution environment. I don't know how I didn't pull out all my hair back in the C-in-Unix day when we had to explicitly free() stuff, trying to track down those couple of obtuse memory leaks that /always/ found their way in somewhere....
(Edit: Unless you like doing your own heap management, I guess. Diffrn't strokes and all that, I suppose, but I find that I get a lot more done per unit time without it.)
Anyway, I think if you want to write portable software, you're better off using an inherently portable language like Python, Java, or C#. It is unfortunate that Apple has chosen a licensing scheme that makes using such languages on their handheld platform difficult. :<
I chose Java meself, explicitly because there are some tools in development at Google for compiling java apps down to native arm code that can be distributed on the Apple store and installed without rooting the machine. The tools are still a bit too immature to mess with at the moment, imo, but I am hoping that they'll be pretty decent by the time I get this particular project complete enough to start thinking about porting it to something other than Swing and Droid.