this ps3 xbox argument always comes around i own both systems and they both have their own strengths but in terms of graphics from my opinion the ps3 has definitely got the edge killzone 3 too me has been the best looking fps to date on a console but the xbox is so close it's really not worth splitting hairs over plus id never argue against the online on the xbox being superior.
Its not really fair to compare a subscription service to a free service though. Out of the box the ps3 can be used for online play but the 360 can't except for a trial. Over 5 years you have effectively paid for the console again with xbox live. For pc, ps3, wii and wii u it is a free service.
If your going to compare like for like then surely you must add the cost of xbox live for the likely length of ownership. So effectively a 360 console that you use online for 5 years needs £150 added to its purchase price for the comparison against the ps3's price and then you can say the online service is better. Also lets not forget PSN plus also offers huge additional benefits and can be had for £30 a year and gets you a huge amount of free extra games to play. You could add that in for comparison and the PS3 looks far better value again.
You can basically own a 360 and a PS3 for the same price as a 360 and xbox live for 4-5 years.