Over the years I have had many different monitors, with many different set ups. Of which I use for gaming and also for professional work. So I figured I would give pros and cons to each different type of set up that would be universal to any set up using the same configuration not just my specific hardware.
Eyefinity with 3 exact same 24" 1080p monitors
1. Lots of screen space
2. Fun for certain types of games(racing, 3rd person shooter/rpgs, some First person shooters)
1. Many games don't support eyefinity even with 3rd party software
2. Needs SLI or Crossfire, or really high end card to obtain decent framerate on AAA games
3. Programs such as chrome will expand to all 3 screens unless using a snap grid like hydra grid(ati), does not snap to each monitor like if you have just 3 screens with no eyefinity
4. Micro stutter is more noticeable on sli or crossfire
5. LOTS less desk space
6. (ATI specific) Needs active adapter for at least one monitor
Conclusion: While eyefinity can be alot of fun for games, the number of games that use it is small, and the number of games that use it well is even smaller. It can cause alot of hassle outside of games for just everyday tasks, and can make multitasking harder even. I specifically had a harder time with this one because it doesn't really leave space for speakers and I'm big music person.
Single 30" Monitor
1. Higher Resolution(2560x1600)
2. 16:10 Aspect Ratio(better for games, although some ports don't expand for the 16:10 aspect ratio)
3. Lots of retail space
1. Requires card that can drive double resolution of 1080p, not as taxing as eyefinity though
2. Expensive no matter what monitor you get
3. Hard to find fast response monitor for a reasonable price
Conclusion: This is personally my favorite set up by far(although part of that is that I splurged for a wide color gamut and fast response monitor). Many other set ups come with alot of hassle, this one keeps it simple while giving a hybrid of screen space to performance. The increased resolution really makes a difference. The Aspect ratio is more pleasing to the eye when playing a game(golden rectangle). Great for professional use if you spend the money for a color accurate one.
1. Most retail space of any single monitor
1. Many games do not support 4k and some outright won't play
2. Requires 2 inputs normally
3. Actually 2 vertical screens for most 4k monitors resulting in weird displaying sometimes when fullscreening
4. Technology is not there for picture quality or response time
Conclusion: I would only get a 4k monitor if you need more space or want to see something larger than even a 30" screen, and even then I would still advise a 30" screen because most are not much larger and you will take a larger performance hit. Good for meetings if you need to display to a group of people.
Two 24" 1080p Monitors
1. Lots of retail Space(Less than eyefinity, but more than 30"
2. One of best solutions for multi-tasking
3. Lots of retail space for the money
4. Same performance as single monitor for games since it displays on main screen
1. Less desks space(takes up more than single 30")
Conclusion: This is a great solution for people who don't want to spend a lot of money but want extra retail space. Also great for multitasking such as watching a video while playing a game or keeping track of a stream while streaming. There really isn't any reason to not get a second monitor unless you don't have the desk space, it makes it easier to do a multitude of things.
If you have anything to add that I may have looked over or if you had a different experience let me know.