no contest 550d, it will take good pictures i have one so i know. look at the ratings for both cameras here on this site.
my advice would be get the 550d plus the kit 18-55 lens then see what you need later onc eyou get used to the camera;
defo the 550d, image quality, video and low light performance are all surpass the panasonic, plus you've got the choice of around 70+ lenses, compared to the small selection of MFT lenses.
It might be worth your while waiting a couple of weeks, with canons 60d just being announced, and nikon set to show the d7000 (d90 replacement) there are definitely some great cameras on the way (oh and dont forget the sony a55/33 )