I have used all three, plus Rowley CrossWorks and command line GCC. As you would expect there are pro's and con's to all.
I would suggest making a list of what you want the compiler to do and cost, THEN obtain demo's of all the options to see which suits you best.
As far as benchmarks go - are you interested in size or speed? Or are neither of importance if your processor is large enough? The presented benchmarks tend to contradict each other. The most important thing to you might actually be 'how reliable is the compiler', and benchmarks don't tell you that!
I would second that. I'm in the process of porting three projects from IAR to Crossworks
For my initial tests I could not see any significant difference in preformance between the GCC and IAR compilers. The GCC tend to generate slightly bigger code though (5-10% bigger) but in my application that's not a factor.
Rowley offers a 30-day trial. Try it. If nothing else, the IDE is a LOT better then IAR's - and much less buggy!