Ok this is for serious, subjective, non-biased replies...
I love my 5D Mark II, since I first started pushing the shutter on it over a year and six months ago, I've loved it. I get amazing pictures most of the time, and have gotten great responses from many of my friends on my photography.
So I'm not hating on Canon or my camera, but lately (past 3 months or so), I've been really starting to get picky with my photography tastes, my own and others. Seems I'm starting to realize what I like and don't like, what is camera and what is post processing etc. I know that the 5D Mark II is up there with quality, and the camera of choice for many pros, but I'm starting to notice a lot of Nikon users in the same photo styles that I'm into.
So what Nikon is the rival to the 5D Mark II? The D700?
What does the Nikon D3s rival in the Canon world?
I'm starting to mold my photography into a children/family based lifestyle photography, and feel I need some quick bursts, full frame, good mps etc...basically the goodness I'm getting out of the 5D Mark II but maybe a bit faster?
Are these higher up Nikons revled in the camera world as portrait cameras?
Where as Canon is well known for its sports/action stuff?
Or is that just stereotypes?
Should I consider an upgrade to my Canon body vs. a switch/upgrade to a Nikon body?
I know this is a sin to discuss on a Canon board, which is why I'm looking for subjective replies. I was sold on Canon the day I held one vs. the Nikon, and haven't had a second thought. But now maybe I am? I've seen plenty on this board to not have these issues in my head, but what's getting me is whats coming from my camera. Maybe I need to relearn it, or start back over in Photography 101, or something. I just feel some of the stuff coming from my camera lately isn't up to my expectations.
Has my pickiness with what I think is good/bad photography blinded me and what I'm doing and creating? Am I being too hard on myself? Have some of you gone through this phase and questioned your gear?
Maybe its time I bought some L primes and found some good stuff coming from the 5D Mark II? I have two L zooms, maybe I need to prime up?
EDIT: Since posting this, the following replies have help me come to the conclusion I don't need to switch, thanks to all who have given great inputs.

