I have both, plus Chessmaster 10 and I use all three, as well as Chessbase 11. To me, you can never have enough chess knowledge at your fingertips, but a chess.com membership puts everything all in one nice and neat little package. Fritz Friend Mode is what I use to play against but all of the training videos and articles here are awesome too. I'd say if you had the cash, get both, Fritz is about 50 bucks or less. But I think the Diamond membership here would do more in the long run. 
-Mark
I have Chessbase Free version so i get to play against Fritz 5.32. Problem is, it's the free version, so yeah... no extra bells and whistles. What do you think of Chessmaster 10 compared to Fritz? I think I am going to get the membership... It seems to me, it's about time for Fritz 13 to come out anyway... 12 has been around for 2 years already, no?
The other reason to get Fritz 12, is the 1 year membership to Playchess.com, which I would like to think would be just as good as a membership here, and it's half the price of a membership here. But as you said, if I have the money, I should get both... lol
So I've been a Fritz user since Fritz 8, and have had every iteration up to Fritz 11, but now I'm debating whether to buy Fritz 12, OR get a 1 year Diamond Membership on Chess.com. Both have a huge database of games, both have online chess servers, and both have huge communities. Obviously many of you have both a membership AND Fritz 12, or another awesome Chess Suite, and really, I'm looking for what will give me the most personal improvement in my game.
As an aside, my whole family loves chess. My 12 year old son is getting better, and still says I'm the only one who has ever beaten him (this is laughable...) so I want something that will not only help me with my game, but something I can say to him, "Here, go play against Fritz for an hour" or "Go read the forums and look for the <Insert Opening Here>... study it."
Which has better tutorials and training available, and will most improve our game, Fritz 12 or Chess.com membership?