Depends on what you play and if you want to wait to play it. There is a lot of factors you have to look at..
Online:
There is no way anybody who has an P3 can even think to say that online is better on a P3 than a 360. I could go in detail but do I really need to? Xbox live is by far WAY better than anything Sony has to offer. Ok it is free big deal that $4 a month does not burn a hole in my pocket. You get what you pay for plain and simple. Not to mention there are games that came out in both the P3 and 360 yet the P3 DOES NOT have online play.. Matter of fact there is more than a few games that are like that..
Games out:
Again P3 is way behind.. Yes I know that the 360 has been out for a year longer.. But, look at the games coming out for P3.. They are STILL making games for the P2 and the bad thing is these are games that might not even be out for 6+ months. Why? because P3 sales are bad. There is 3 times(17.7 mil to 5.5 mil) as many 360's as P3s. So there are 3 times as many buyers buying games. Again yes I know that the 360 has been out a year longer but the 4th qtr of 2007 the 360 sold almost 5 mil consoles. By the way thanks halo 3. The Wii and P3 were released at the same time and the Wii is right at 8 mil in sales. But this one is easy.. Go to Wal-mart and just look at the games section and that will give you a good idea of how the P3 is doing. There is a lot of games that the 360 release and then it takes the P3 3 to 6 months to release. That is NOT ok in my book. The console has been out for a year now and that is NOT acceptable to STILL be that far behind.
Connection:
LOL who cares if it is wireless to the internet? I don't run mine wireless there is no need to. If you really needed wireless, you could always get one on-line. I'm sure the cost difference between the 360 and the P3 would more than cover a wireless connection.
Movies:
Not really getting into this again but yea if you want to buy a console to watch blu-ray movies, than the P3 is your console. The 360 you will need to spend the extra $100 (on ebay all day long at around that price) if you want to watch HD-DVD movies.
Future: It is rumored that xbox will release their new box next year. That would put xbox 360 at 3 years old and time to release something new. P3's problem is it was pushed to far back and buyers who wanted top of the line gaming console HAD TO buy the 360. Then they release at the same time as the Wii and got outsold by them.
The only thing the P3 has going for it is the fact that it does play Blu-ray discs. If they didn't have that, they would be dead and buried.. Now they are just on life support...
But.. of course... I could be wrong..