Not being much of a multiplayer fan, I'm not going to answer this question. I'm merely going to present it to those who routinely experience both the free PlayStation Network and the paid Xbox Live service.
We have PlayStation Plus now but it's optional, while Xbox 360 users must still pay to play games online. Towards the start of this generation, most gamers claimed the $50 charge for XBL was well worth it, simply because it was a more fully realized online service. The Network didn't have all the bells and whistles and as a result, many just said, "Yeah, it's free but it's just not as good." Well, several years have passed and the PSN has seen quite a few upgrades and updates.
So as of now, are the PSN and XBL just about similar? If so, that would make the Network more appealing to late adopters, right? Selling a machine to a casual gamer would be easier if you could just say, "And playing online is free, by the way." Then you could add that essentially, it's the same service as the paid Live subscription, so you're not really missing out on much. But is that truly the case? If not, what's still missing from the PSN that makes it inferior to Live? And is that lacking worth it for you to pay for Live? Is this still a "you get what you pay for" situation?
Personally, I'm not involved enough to tell the difference. As far as I can tell, you go online to play games with both services, and one is free while the other isn't. I don't really have any problem using either service, so… But as I said, I'm no expert.