Both can be good, in general for larger tanks a closed loop can be a cheaper alternative. Here's one I did on a custom 270 gallon:
Pump outputs were placed through the bottom pane and the inputs on the back to avoid sucking in sand. Also I went with two inputs rather than one single to reduce the suction velocity.
I also installed a 4-Way OM and mounted it sideways over the sump for easy maintenance which is key for such a system, you need lots of space otherwise it's just a headache waiting to happen.
The outputs where covered with rock using some zip-ties .
So you do get a clean look with the closed loop, but it will probably use more power than a tunze setup. However a tunze setup is going to cost a little more but if you plan ahead you can generate a clean look this these powerheads as well. I've always liked the idea of making your tank a little wider and building an acrylic curtain in the back and placing the tunzes behind the curtain alowing only the nozzles to penetrate into the visible tank area through strategically placed holes.
A tunze setup will also give you more control and better alternating flow. In my tank I use both, a closed loop to produce the majority of the flow rate and a tunze to provide a short right angled wave and better water alteration.