Should I go for a 4k monitor or an ultrawide 3440x1440p monitor?

Putting together my first build. I'm looking to have a really good gaming pc and also a good pc for video production. The two monitors I'm deciding between are the Acer Predator X34 34.0" 100Hz Monitor http://pcpartpicker.com/product/WDcMnQ/acer-monitor-umcx1aa002 or the LG 31MU97C-B 31.0" 60Hz Monitor http://pcpartpicker.com/product/wykwrH/lg-monitor-31mu97cb