If we are soley debating the features of both, i'd have to say from my opinion that the PS3 has totally dominated XBL, the layout of the Ps3 is easy to use (XMB) compared with the xbox dashboard (imo i think the dashboards way too cluttered, i prefered the old dashboard).
Xbox was the first to offer near enough everything before anyone else, thats because microsoft is such a huge company they just outright buy the rights to do so whenever they feel like it. Also since Xbox doesn't use Blu-ray, game makers tend to sway towards making games for Xbox as it requires less skill and know-how, so the quality of ps3 games isn't always how it should be because half the games are originally made for the xbox and ported over to the Ps3, this is why games are released on xbox earlier than ps3 in 9/10 cases.
Feature wise, Xox is rich with features, you've got cross gaming chat, the ability to jump into chatrooms and chat with friends whilst playing a game, you have the Xbox avatars, XBL arcade with some awesome games in there, and the ability to customize your gamertag a little more than you can with the Ps3 gamercard (aka setting your game type to: Pro, Recreational, Family etc etc).
On the other hand, Ps3 offers an extensive array of things such as the mighty Ps HOME which is a free online roaming social RPG type thing where you can create your own avatar and connect with others through simulation (think SIMs) you can decorate your own house, buy new houses, clothes and other things through shops that are within HOME for a small fee. in home you have an extensive array of free games to play, as well as finding out about news and upcoming titles through the ad boards. XBL doesn't offer this or anything like it.
Ps3 also offers an online browser which XBL doesn't which for saying microsoft near enough own the internets, you'd of thought they'd give you a browser in there consoles.
Ps3's store layout is fantastic, also you can pay an optional £40 a year subscription to have access to 4 free games a month ontop of some extra features like automatic downloads, theres also option features like LOVEfilm, and an itunes type music thing which you can get.
you can automatically post any Ps3 trophies you earn to facebook (not sure if this is possible with XBL)
Online gameplay is very good on PSN and although PSN users don't get dedicated servers like some XBL titles, theres not much conectivity issues with most games, HOWEVER XBL users get better conectivity because of the large playerbase it has.
i really wish PSN would allow users to cross game chat like the Xbox, but i can't see it happening in the near future.
On the whole, PSN is totally free and will be for the foreseable future, it makes its money through the optional subscription and discounted games you get through your subscription and the ads within HOME (and all the things like LOVE film and the itunes type thing). This is where XBL falls as it charges its users to play online whilst giving them ads and things that they don't want to see, with PSN theres literally no adverts anywhere unless you go into HOME and view ad boards while roaming around.
Microsoft needs a better way to market XBL, charging to play is not the way to do it. if you can afford the extra £50 a year then thats great, but i'd sooner spend that £50 on a game or buying a PSN subscription and get 4 free games a month
I don't mind waiting that bit longer for titles when i pay nothing to go online with them, i guess you could say XBL premium is so that your paying for your titles to be released first and to have more Exclusive titles.
When i had my Xbox i loved GoW and halo, but since i moved to ps3 (which i was always gunna do anyway since i'm a big ps fan having a ps1 and 2 previously) i found that Ps3 had some awesome exclusives too like Resistance and Killzone, Devil may cry, Metal gear solid (back in the day) along with some big titles im a massive fan of (Final fantasy being the main one).
Also another thing, if you don't own a FAT ps3 (60GB with backwards compatability) you can simple buy most of the good ps2/1 games from the store, meaning you've got a hell of a choice of games.
also from rumors i've heard Sony plans to re-release some old skool games with trophies (like Devil may cry 1-3 and the old metal gear solids)
so for me i'd say PSN is way ahead at the moment.