i have both, ps3 launch system still going strong (getting a bit louder now tho lol) and an old style xbox!
i prefer the PS3's interface as the latest xbox one is just too much! its probably one of those things that once you get used to it then its fine.
i use the PS3 more but i do have the same issue as you mate, all my friends have xbox's so online im a bit of a lone wolf and on Starhawk thats proving a bit of a disadvantage as theres an awesome game but it requires communication to fully enjoy online imo!
the Xbox has some great games and the third party multiplayer ones i always get for xbox just due to the online with friends etc however! the ps3 has soo much out now and a fair few exciting projects in the near future that if i had to make the choice you are making, i would keep my ps3.
my Xbox gets little to no use anymore but i dunno why! i may get max payne on there so i can play with my buddy's but these days its all personal preferance like i really prefer the feel and weight of the dual shock ps3 controller as the xbox one feels weird to me, but then the next guy will say the opposite!
xbox requires additional; costs as some mentioned above, to play online leave urself like £40 for a year of live (its a great service IF you take advantage of all the other bits your paying for), rechargable battery pack for the wireless controller will be needed or use a wired one or swap AA's out quite often (really suprised thats not included yet)
but yea both have there ups and downs, depends what you play, what your friends play, and if you want to play online with them or some uinique exclusive single player games this year.