You keep what you enjoy.
I would never give up Nintendo for Sony or Microsoft. Their games have never failed to entertain me.
Their core franchises have always been fun. Sure, some of them have been lacking recently (mostly Mario and Metroid), but the others are still going strong. We're getting a new Zelda next month, with the new Wii U console we're getting Pikmin back, a new Super Smash Bros. for both Wii U and 3DS in the future, as well as many others for these two new consoles.
Their third-party may not be that great, but their first-party can't be beat (personally speaking).
I would rather miss out on "amazing graphics", shooters, and the online-capabilities than lose the console line that has given me my most precious of memories with video games.
Now, their recent consoles haven't been incredibly impressive. The 3DS is just a souped-up DS with an interesting feature that some can't use (regardless of that, DS games are fun. with power it has been given, some nice games are coming along in 2012), and the Wii/Wii U is primarily motion-control (yuck). But neither of them are a deal breaker for me.
If the situation is a lose-one gain-one, I'd stick with Nintendo.
If they just want you to try out the Xbox, give it a try.