So if you want two monitors, one 5K monitor is out. You have not specified what "best" means to your. Is it lowest price, best reputation, % of sRGB gamut, % of Adobe RGB gamut, off asis viewing you can do with IPS panels, faster refresh rate you can get with TN panels that will do better for gaming than slower IPS panels.
Describe your use case and requirements.
Of course: I want two monitors and 5k is not important to me. Even the resolution of 4k is probably more than I need. I just use for daily internet use, streaming, etc. Most important to me is getting resolution up above regular 1080 that I get on my current two Samsung 27inch Syncmaster P2770HD's. I want resolution similar to the retina display that is currently on my mid-2015 Macbook Pro - I have the 15 inch with the dedicated video card so I believe I can run two 4K monitors from the display ports at 60hz. Price isn't a huge issue. I would just buy the apple TB display's if they weren't so old and out of date.
The Dell you mentioned is a good price, but they aren't great aesthetically. Am I missing anything out there with a good look? Is this one of my better options?
http://www.amazon.com/Samsung-28-Inch-Definition-Monitor-U28D590D/dp/B00IEZGWI2
Thank you for the help.