Nintendo is incredibly out dated when it comes to their online distribution. I'm surprised it took them this long to finally do something like this when it should have been done since the Wii. Playstation didn't implement the PS Network until the PS3 came out.
Playstation has the best online service
Then Xbox.
Then Dreamcast.
And Nintendo falls in last.
I'm not quite sure how Nintendo falls in last. Especially when you're only talking about the latest systems.
It's free.
I have never experienced unexpected downtime or heard about any security breaches.
On the devices themselves, you can access the public communities. You can go into game specific communities and post things on the boards. This is between both the 3DS and the Wii U, and you can even somewhat access this on the PC.
I never had to deal with some kid screaming into the mic (something people on Blockland always talk about when mic support gets suggested!), nor did I ever have to deal with some salty stuffhead messaging me about stuff I don't care about.
The only lag I've experienced was when it was between players, in games that are peer to peer/player host networked. This isn't a problem with any platform, just the software you choose to run on it. This happens in many cases on any platform regardless.
Other consoles have stuff choices for multiplayer games (split-screen and online), unless it's something that's on PC as well.
PCs cannot have the best online service because it's not a service. It's just open. No connecting to XBL/PSN/Nintendo or anything like that before you can do anything. It would be the best if it was how it is but it was for some reason a service. But it's not a service, so it's not the best service.
So the best would have to be Nintendo.
Rest are irrelevant or outdated.