Looking at the sales it's Sony, no doubt.I don't see anyone else who kept a baseline of 80 million in all their generations.

I'd say Nintendo fans are the most loyal, since a good amount of PS4 sales came from switched over Xbox fans.

I disagree since many PS2 fans switched over to 360.

SEGA.

Old SEGA, I mean. The SEGA of MegaDrive, Saturn and Dreamcast. The SEGA of innovation and creation. This company doesn't exist nowadays.

I think Nintendo is the company with more loyal fanbase. Maybe not in Europe (probably Sony wins here), but they release the same IPs since the 80's and people is still buying their products. I think they don't deserve it.

It's about the biggest loyal fanbase. Looking at the numbers Sony had lots of fans to spare and still retained the biggest fanbase. Most of Xbox's fanbase today came from PS2 and yet PS3 retained a high level of sales.

Who else managed that? Correct, no one. Nintendo never had a huge steady fanbase and Xbox is one generation too young to judge loyalty. It's a win by numbers not feeling.

it doesn't say "who has the biggest fan base", the OP is asking about which fan base is most loyal. Losing almost half of your fanbase even if you still have the biggest is not having the most loyal. If they were loyal they wouldn't switch. 

Nope. I checked throughly before posting. I too wondered if it were about the numbers or the grade of loyalty. The OP clearly says:

Who has the biggest loyal fanbase?

Unless "big" is now an adverb describing loyalty it still means numbers. Since it is impossible to say how many of the sales were made by loyal fans we can only go by the lowest baseline sales and that contest is clearly won by Sony.

If it were about the biggest fans I'd say Nintendo because their games are deeply ingrained into their hardware while Sony's and MS's consoles are just vehicles to get to the multitude games.

I'm kind of shocked that people are voting anything but Nintendo. We know that much of the Playstation and Xbox fan-base have switched before. Many Playstation fans, including myself, were once Nintendo fans. Quite a few Playstation fans have switched to Xbox and vice versa.

Nintendo purists, on the other hand, will buy a Nintendo console as long as a trickle of the usual franchises keeps coming, even if there are next to zero games being made by outside studios. That's the epitome of loyalty.

I was reading the title when I wrote that. But yes you can get an idea of the loyal fans since its about games too. Especially when Nintendo first party has a good constant of high attach rates. While Xbox and PS get a good amount of their tie ratios from 3rd parties.

Or Stockholm Syndrome for a company that holds their favorite games hostage ;)