Hey Sylar
Not going to be too helpful I'm afraid as I've only really used Canons out of the two. TBH I think you'll find getting that answer about as easy as going to a tech blog like engadget and asking in the comments section "who's better - Apple or Microsoft?"

Maybe without quite as much animosity, though
Just wanted to suggest you have a look at micro four thirds cameras if you haven't already. My mate's a professional photographer (more fashion/editorial than wildlife) who uses a Canon 5D mark 2 with the kit lens. She recently picked up a Panasonic GF-1 with the 20mm pancake lens, with a view to having something more portable but still capable of near SLR quality images.
I've played around with it a bit and it's a lovely little thing. I'm sure it'd be larger with one of the zoom lenses but nothing like the 5D. In terms of image quality it's really not far off to my eyes, far exceeding anything I've seen from another camera of this size. Good low light too. My mate has found she uses it more than expected, as it's so dinky it just goes where she goes
Obviously, getting a GF-1 with a couple of lenses is going to set you back nearly what a Canon 550D kit would cost. I only mention it as the size difference is significant and, if you're going to be creeping around outside, it might be worth a look
Z.
This post has been edited by ZedBud: 10 May 2011 - 01:26 PM