This list is not nearly as in depth as some others, but there is a whole lot of reasons why xbl is better. I'm comparing Free version of PSN. There are some big things that make XBL better like party chat and faster downloads, but it's the little things that go unnoticed that make a difference
True Skill matchmaking: Matches you with players that are around the same skill level.
Cross game chat: Chat with anyone any time.
Voice messages: Send voice messages.
Party Chat: 8 people in a party playing, watching, or doing whatever you want.
Background downloads: Download items while playing games or doing whatever.
Faster and better connection: Downloads are fast, finding games are faster, faster updates and less lag.
Player profile: player bio, gamerzone, etc. You can see more in depth of what games people are playing with details like what game type, map, etc.
Playing with friends: You can have more than one person log into XBL on one Xbox, while you can only have one at a time on PSN.
User friendly: A lot easier to navigate then PSN especially for casual gamers. The dashboard is a lot better implemented onto XBL to make it fell like it's all one thing.
Demos: A lot more demos. Every Arcade game and Indie game has a demo along with most full retailer games have demos.
Arcade games: More and better arcade games on XBL. Almost or all arcade games have leaderboards to compare against friends.
DLC: XBL has more DLC support and usually gets DLC first via COD and Fallout.
Re-downloads: You can re-download anything as many times as you want if you delete it. Can’t do the same on PSN.
Apps: Twitter, Last FM, and ESPN.
Deal of the week: Weekly deals and there are awesome deals during holidays like Christmas or most recently April 1ST
Kinect Video: Live video chat with anyone.
Yearly updates: XBL has had HUGE yearly dashboard updates to improve XBL and make huge drastic changes. PSN does have more frequent updates, but not nearly as big.
Videos: There is MSNBC, Major Minute, Kinect Show, isentuamessage, talking with tina, IGN strategizer, and other videos you can watch on XBL from the dashboard.
Game with Fame and Developers: You get the chance to play agianst famous folk and you can play with the developers.
Netflix: I know PSN has Netflix, but it runs better on XBL along with parties you can watch with friends. You can also see what movies your friends are watching.
Game installs: Game installs are optional, but you have the choice to install every single game you own to make them run faster and smoother.
Population: More users on XBL. You have a better chance of playing against different people on XBL.
XBL rewards: If you join the rewards program you can get free MS points and have chances to win pretty big prizes.