Nintendo

+1st party games are quality assured
+1st party IP's have good variety
-Virtual console for Wii U and 3DS has not delivered so far

PlayStation

+Gets most JRPG'S, good japanese 3rd party support overall
+Vast game library with good variety
-Jak and Crash are dead

Xbox

I really don't know

I don't think I have a bias for a particular company

Nintendo
+ Great first party games
+ Innovators of gaming
+ Quality games that dont need no patch
+ Hardware that lasts
+ Fun for all ages
+ Doesnt conform to modern gaming
+ Supports two concurrent consoles

- Terrible third party support
- Poor digital/virtual console support
- Weaker hardware specs
- Doesnt accept modern gaming
- Region locking is lame

Sony
+ Great diverse library of games
+ Decent first party games
+ Understands the modern gamer to an extent
+ Good console specs

- Quick to copy other companies
- Quick to conform to the trends
- Terrible handheld console support
- Online is buggy despite now costing money....

Microsoft
+ Pioneered online gaming for consoles
+ Strong online
+ Good place for FPS games I guess.....
+ Third party support

- Lacklustre first party games
- Began paid online model
- Consoles not really built to last
- Trying to force all things that arent gaming onto gamers

So yeah... about 70% biased to Nintendo

I dont care enough to be biased. I generally like Nintendo and Sony, and never really got into contact with MS console gaming.

Generally I like Nintendo for good family friendly games and Zelda, which was a big part of my childhood. Generally I like Sony for being what Nintendo used to be: the home of great 3rd parties.

Back on the SNES, we had the best of both. That was great.

I try to troll them evenly..

100% unbiased.

I'm biased towards the best console on the planet. What can I say I like the best of the best. I've a healthy respect for Nintendo and pc too.

Wow, and I thought I was biased!

I'm not unbiased, nobody is.

Nintendo Pros

1. Nintendo games are amazing, unique, polished, ship with minimal bugs and you can't play them anywhere else.
2. The Mii-verse is the friendliest online social network I've ever seen. Love the artwork people put out there and the general good vibes. It's refreshing and makes me appreciate the heavy moderation rather than resenting it. Not to mention free internet?
3. Whether people like it or not N is constantly innovating and trying new things. The industry needs this type of thinking even when it flops. I personally love the game pad and thinks it adds quite a bit even when the games use it for simple things like displaying a map. I mean how nice is it to be able to play a game like Batman Arkham Origins and not have to pause the game ever minute or two to bring up a map on a menu screen.

Nintendo Cons

• Reward programs to this point have been nothing to write home about. Hopefully Club Nintendo's successor will remedy this.
• Hardware could be better - Not being able to plug a CAT-5 directly into my router really sucks... adding additional storage is great but the fact that it has to use an additional power source or take up both USB ports is problematic.
• Nintendo Accounts need to be unified between platforms (3DS/Wii U) on a wide scale

Microsoft Pros

• XBox Live is the best console experience for online gaming.
• Rewards are incredible, in a way they are too good! I haven't upgraded to XBox One yet because of the amazing free games that I get every month on the 360. Most recently I can't wait to finally try Witcher 2 a Brothers: A tale of two sons.
• Most successful in expanding the console experience past "just games". Movies, TV, interactive TV, connecting to your PC, etc. 

Microsoft Cons

• Exclusives... Halo? Sunset Overdrive? I don't really care.
• Why do I have an Xbox when I can play the same games on PC or PS?
• So far have failed to tap full potential of Kinect.

Sony Pros

• I love RPG's, Sony has strong exclusive RPG and story based content in general
• Handheld consoles are severly underrated. 
• PS Now finally becoming something worth while

Sony Cons

• Majority of the library can still be played on Microsoft's console as well
• Potential for full integration is limited when compared to MS (MS has advantage with by being able to leverage Windows/PC's)
• PS4 library has been slow to build up

Nintendo
+ Strong commitment to polished releases
+ Focus on "play"
+ Comittment to IPs
- Regressive attitude towards medium
- Willingness to stagnate
- Lack of market awareness

Sony
+ Strong market awareness
+ Diversity
+ Willingness to take risks
- Tendencies towards over-commitment
- Lack of identity
- Underserved online infrastructure

Microsoft
+ Embracing media convergence
+ Willingness to specialize
+ PC
- Slow to adapt
- tendency to over-specialize
- Image