I agree with LP's points: listening is key. I'll add a few more from my own (also) limited experience.
* I like the M-Audio line because of the monitors' very helpful adaptability for different, imperfect home studios, like mine. There's even a bass cut-off switch, with 3 settings, that allow you to integrate a sub effectively, which I did. These switches really make a difference, and they contibuted to my choice of M-Audios.
* I did buy and compare 3 different monitors in my own studio (including the active Alesis Ones). Listening really does make the choice much easier since personal tastes are so important.
* I read a lot before I bought. Search the pro mags, particular. Future Music, for instance, recently had a pro monitor shoot-out, which included the M-Audios you mentioned but not the Wharfs.
* Search this site extensively. There's a ton of opinion already written recently about each of these monitors you're considering. People here just get tired of repeating themselves.
I'll also add that you shouldn't overlook the BX5s, which Future Music's shoot-out rated highly for overall accuracy. You probably will need a sub, though. I easily added a Whafedale PowerCube 8 ($99 online), and the sound is truly excellent for a budget system. In fact, I'd put my system ($370 retail) up against anything double its price--it's that good. My mixes are translating beautifully now, and the sound is so good that I'm using the system more than my expensive home stereo for casual listening. Sparkling clear, smooth, punchy, with solid extended lows. I did have to spend some evenings working with reference CDs to tweak the set-up so that the freq response is seamless. Adding the sub, though, really brought the sound alive.
Even with the BX8s, you might want to add a sub later, so the switches that allow this addition could be useful someday, even if not now.
Aside from that, I hear the Wharfs are also great monitors. I know that their cheap sub is so much more than I expected--no mushiness or boominess there. I'm led to believe that Wharfedale is a fine company, and I know that Deepwater is a respected guy to order from here. I might have done so myself if the Wharfs had been available from him a couple of years ago.
Hope my rambling helps in some small way.
Best,
J.