Depends on what you think it's best for you and the games you're going to play.
Some games benefits with triple monitor setup because it gives more field of view, where you can see more of your surroundings, that wasn't possible with a single monitor setup, while other just enlarges the image through out the 3 monitors.
For some, that line when placing the monitors together might be a issue, even if some monitors manufactures try to make their bezel as thin as possible.
Here is a list of games that supports AMD Eyefinity and Nvidia Surround triple monitor setup. It also tells whether if the game benefits with triple monitor setup (more field of view) or just enlarges the image which doesn't benefit with triple monitor setup.
http://www.wsgf.org/mgl/ef_s/
If you're going with Nvidia surround then look at monitors that can do landscape and portrait mode, this gives you more options for Nvidia Surround setup, as some don't like their monitors in landscape and would prefer portrait.
If your getting a triple monitor stand then it doesn't matter what monitor you get. You can mount it the way you want.
Just make sure the monitor has VESA mounts (those 4 screw holes on the back of the monitor) or else you won't be able to mount it to the stand.