I'm fairly new to brewing and I'm in a 6 month long college level Science of Brewing class and have brewed several batches. Pretty intense course that has 3, 1 hour long lectures and a 5 hour lab every week. I have five instructors in the course one is a history professor and the others are bio chemists all of which have brewed for nearly 30yrs each at home. We uses some pretty simple setups to brew and one of the most simple effective setups is our wort chillers. We use a 20ft length of 1/4 copper tubing coiled and the coils are spaced rather than compacted in an effort for the cold water and ice to isolate and cool the hot lines. We use our mash tun cooler as our ice bath. Simply throw the coil in and fill it with ice and then water to about an inch from the top. (3gal cooler). Hook up the lines and start siphoning the wort. It's fairly important to grab the output of the chiller and bob it up and down in the bath about a half an inch. This keeps the fresh cold water circulating. Doesn't take but a few minutes to chill a 5 gallon batch. We actually had a problem with our wort only being 40 degrees and was too cold for our yeast and had to wait for it to warm up a little bit to an effective temp for our yeast.
We also had a discussion about immersion chillers in which you pass the water through the chiller and dunk the chiller in the wort. All of the instructors advised against it mainly because of sanitary reasons. Yes yeast needs oxygen often missing in home brews but they state through numerous experiments there was not a significant increase in O2 in the wort with this method. The risk is much higher of getting a bacterial infection etc in your wort by dunking the coils in this method not just from the atmospheric but also from the coils themselves. Copper scratches easily and bacteria can easily hold up in those areas and pass into your wort. It is more difficult to scratch the inside of the tubing and is easy to maintain the sanitation. Simply flush it with PBR followed by Star Sanz before and after brewing and hang upside down to clean.
This is the one I just built for myself with $20, 3/8 in 20ft copper tubing, $3 spring pipe bender and a few zip ties. We also use quick connects, cheap, effective and easy to replace frequently to maintain integrity. I have mine built so that if I need more tubing I can simply bend another length, attach it with a quick connect and strap it to the output like the rest of the coil to secure it. This is going to utilize a 5 gallon cooler for the bath. So IMHO running the worth through the chiller is the way to go.