i run into this question all the time at work. myself, i prefer the comp route with a good coax. digital audio cable. true, a 1080p (native or upconverted) is not '''likely''' possible with a comp cable, however i feel the difference at normal viewing distances is almost not noticable. (infact, my boss said he would pay for your TV if you could pick out a 1080p vs. 720p picture at appropriate distances.
***disclaimer, this is not an official challenge, i dont want every eagle eye calling my boss to take him up on this***
back to the lack of 1080p with comp: manufactures of DVD players heard that comp inputs on a TV couldnt handle 1080p. Then TV's could, but only after DVD players stoped being able to output 1080p with comp. and this trade happened a couple times. this is my understanding of why comp. doesnt send 1080p. i do believe some players can upconvert to 1080p over a comp cable, but i dont know any displays that can handle that...
combine that lack of real obvious difference, with the lack (little amount and pirce comapaired to SD DVD's) of 1080p media (currently) and the fact that hdmi comunication issues (between devices) exist, and the artifacts in some hdmi applications, and the whole hdcp idea, though i understand the reason behind it, will ultimately ruin HD media, and the continuing change in hdmi standards for my reasons behind using component video cables. besides, 1080i is still attainable via comp on some products.
and i will publish my view on the HD/BRD here: i dont think either format will win out. call me crazy. even though HD is quite ahead in the current market, the over all high def media market is around 1%...not to sound like an a$$, but can say SACD/DVD-A? sure they are still around, and might be for a few years, but would you really say they are big players in the overall market...but who knows, with the amount of people who buy things for the latest and greatest factor, and the huge advertisement campaign behind 1080p, my thoughts may be totaly off. hell look at bose.
okay im done ranting, sorry about that.
differences: max res transmitted, number of cables, no audio in comp. (which reminds me the audio transmitted over hdmi....meh, i still think digital audio (coax not fiber optic -- which i a whole nother topic) sounds better.
and just to sound like im covering my a$$, if you dont plan on ever buying another reciever/prepro and/or display, and the firmware for hdmi versions is easily upgraded,, buying hdmi ready gear would be the way to go for future proofing.