CLS are great for adding a lot of flow without a crapload of heat/powerheads in the tank. I could never get the kind of flow with powerheads that I have with my cls running off a mag 9.5. Plus , being external it adds much less heat to the system than powerheads do. Also, you don't have to drill the tank to do a closed loop. Take a look at this one, http://www.melevsreef.com/closedloop.html which I modeled mine off.
All that said, if you have at least a 4' long tank, a tunze turbelle stream with a controller is a really nice option. I'd have one but it's just too much flow for a 36" tank.
The flow with a cls is really nice, I can have it without the heat, PH's falling off and just all the cords and things in the tank. The only drawback I see it a CLS is that with all the angles and head I lose some flow from any giving pump. I have 2 Mag 950 running the cls on my 90 gallon and it is nice flow.I do wish I had more. I also push 1150 out of the sump with a little gaint.
With a closed loop, you have the option of designing the returns to suit you tanks needs. There are several options you can use to vary the currents, SeaSwhirls, SCWD, Ocean Motion devices can help fine tune flow to suit your needs