My little garden is too small to even bother but I do know gardeners who prefer one over the other--more personal preference than anything.  I think Tarnation mentions the highlights.  As for weeds--many place straw and/or newspapers in the beds to maintain moisture and hold down the weeds.  I've seen the gardeners on PBS shows who swear by raised beds but then they're after perfection and probably have (off camera) assistance in maintaining all those beds.