What do you use, and why?
I’m currently using the spring-loaded ball bearing type - http://www.homebrewing.org/12-Barb-Female-SS-Quick-Disconnect_p_1961.html - but considering swapping to the cam lock style - http://www.homebrewing.org/Pro-Flow-Dynamics-12-Type-C-Female-Coupler-Hose-Barb_p_2098.html.
Primarily for use with Chugger pump during mash recirculation and sparging.
Cam locks.
They do not restrict fluid flow. Especially important on suction side of pump.
Easy to clean. No hidden places for crud to collect.
Yep, Camlocks. For all the reasons Phil cites. I use female camlocks on each end of hoses and male camlocks at each piece of equipment. I like that some suppliers provide silicone gaskets in the female camlocks. Those gaskets are well-sealing and durable, in my experience.
Same. Going to be adding fiberglass camlocks to my garden hose fittings too. The spring loaded ball lock type start to grind after a few years.
+1 to what all of these guys said. I’ve been really happy with my Cam Locks (bought from Pro Flow Dynamics and like the gaskets as Martin mentioned).
After reading this I now want to put one on the end of the water hose that I use for chilling so that it’s easier to connect/disconnect when I get to the end of the boil… And maybe onto my water filter and RV hose for pulling water… And maybe in the backyard for the sprinkler too 
GHT camlocks - https://www.dultmeier.com/catalog/0.630.2123
A bit pricey, but I like that they are a different color and different size to prevent mixing.
Thanks, all.
Had a less than ideal brew day a few weeks back, with at least one of the problems identified as caused by the quick disconnect. The o-ring inside a female QD came out and lodged in the throat of the male fitting. Delicious wort started spraying out of the junction and I was not happy. I was having some other flow issues that day, which may or may not have been an early sign of problems with that connector.
I like the looks of the Pro Flow Dynamics connectors, and the fact that they are about 2/3 to 1/2 the cost of the other style (depending on where you shop).
Proflow dynamics has sales all the time. Also check Bargain Fittings, cheap prices and flat rate shipping.
Aside from cost, I’m not sure I’m seeing a problem with the ball bearing sort…
These are what I’ve got, though I think mine came from different vendors…
https://www.amazon.com/gp/product/B00IEFHIK8/ref=oh_aui_detailpage_o06_s01?ie=UTF8&psc=1
https://www.amazon.com/gp/product/B0064OF85I/ref=oh_aui_detailpage_o06_s00?ie=UTF8&psc=1
With being sized for 1/2" ID tubing, I really don’t see any flow issues. As far as cleanup, they flow straight through, with a silicon gasket seal.
Price aside, I think the cam lock/ball bearing debate comes to personal preference. I’m used to this style of connector, it’s commonly used on air tools. Also, no cams to snag open on clothing. I can easily connect/disconnect them one handed.
So, this is what was happening inside my quick disconnects:
The o-rings were warping or dislodging and obstructing the flow.
I ordered some of the Pro Flow Dynamics cam locks. They arrived Saturday, after I was well into in IPA. I swapped out the QDs Saturday night and brewed a stout on Sunday. I like the cam locks so much better! I really liked the solid feel of the connection, the extra length of the barb, barb spacing better accommodates hose clamps, and not one issue with flow rates. I had a a better brew day all around with the stout. I don’t know how much really was attributable to the cam locks, but I sure was a happy brewer on day one of using them.