If someone walked up to me today and asked "Should I buy a PS4 or an XBox One?" My answer would be "neither" go buy a PS3 instead. Based solely on the games, currently, out for the two systems, neither one is really worth it right now. And realistically, neither will have all that great of a lineup until next year (though November usually brings some solid surprises to cash in on holiday sales). However, looking ahead, I'd say that the PS4 is the way to go. Spin away all you want but the XBone has software limitations that the PS4 and it's more difficult to code for. Beyond that, the PS4's exclusives are likely to be much better (Naughty Dog games and JRPGs for example).
I'm not sorry I got my PS4 at launch but I haven't touched it since finishing AC4 back in December. My PS3, on the other, hand is getting plenty of use. Between free Bioshock, Lightning Returns, Dark Souls 2 and Final Fantasy X HD Remaster, it's the only system I'm actually playing. Sony lost the early part of the generation war last time around but they learned a lot from their mistakes and ended the generation in an extremely strong position. Will Microsoft be able to replicate that? Possibly, but until they get some traction going, an XBone is not in my foreseeable future.