It took me a while to figure out how to pick the rotary sprinkler head that is the most suitable for my application. I knew nothing about sprinkler heads a few months ago and now I could replace anyone of them with ease. So this review is written help rookies like me.Here are my thoughts on sprinkler heads in general:First of all, you need to determine if you need 1/2" inlet or 3/4" inlet sprinkler head, which is the size of bottom head to connect to your existing system. You can't mix and match 1/2" and 3/4". Take your existing sprinkler head and make sure you get the right one. If you have the 1/2", then stop reading and do your own research. In general, 3/4" allows for more radius coverage, more range of flow rate, more range to accept your water pressure (psi), comes in different nozzle trajectories, some have check-valve pre-installed, more nozzle options, and at least 2 - 5 year warranty. If you're putting in a new system, make sure you put down 3/4" instead of 1/2"!!!When you need to replace an existing sprinkler head, it's likely that you're going to check with your local hardware store first. You'll find Orbit and Hunter in big H store and Orbit and Rainbird in big L store (as of 2012). I'm just going to focus on Hunter and Rainbird because I'm more familiar with these 2 brands, although you could probably apply the same logic for Orbit heads.Let's go through the top 2 sprinkler heads for residential and top 2 for commercial. I'd recommend install commercial sprinkler heads for your home if you could afford them.Hunter PGP-ADJ, residential:[...]+2 Year warranty+Adjustable distance of throw (decrease to up to 25%)+Adjustable arc between 50 deg to 360 deg+Normal angle (25 deg) and low angle (13 deg) trajectory nozzles. Low angle trajectories are less prone to wind impact, thus they're useful for shorter distances and special shaped landscape where you don't want to waste a lot of water onto driveway.+lots of nozzle options. 8 standard nozzles - may come with the package. Another 12 "performance" nozzles that you could get to fine-tune your flow rate. For example, in a zone where you have a head that covers 180 deg and another covers 135 deg, you may want to set the flow nozzle to "4" for the 180 head and "3" for the 135 deg head to even the overall precipitation. 180/135 = 1.333, 4/3 = 1.333. But what about you have one that covers 180 deg and another one that covers 110 deg? That's where the "performance" nozzles come into play if you're that concerned about evenly watered lawn. Do you math. At last, there are 7 more low angle nozzles that you could buy. I find them useful when heads are next to my driveway/main street AND they don't have to shoot over your fence. These would save you money in the long term as you'd waste less water onto the concrete due to wind.+Errr... that's about it for prosThe equivalent of Hunter PGP-ADJ for Rainbird is 42SA+. Rotation is adjustable from 40 deg to 360 deg instead. Fixed edge is left side instead of Hunter's right. It looks like Rainbird doesn't offer as many nozzles to play around with.Hunter I-20, commercial:+5 year warranty+everything mentioned in the PGP-ADJ that I described above+Automatic Arc Return - will adjust/rotate back to normal if someone bumps into your head while it's rotating.+Non-Strippable Drive - more robust than PGP-ADJ+Short radius and high flow nozzle options+FloStop Control. This is a must have feature for me. It lets you completely stop the water flow coming out of the sprinkler head as you adjust that head while the zone is running. This means you won't have water splashing all over you while you test out different nozzles.+Check valve is pre-installed, whereas on the PGP it's an option only. Typically, if the total elevation difference between your highest point head and your lowest point head is more than a foot or so in a zone, water would flow out of your lowest point head when water is shut off until the water level is below the opening of lowest point head. Check valve prevents this and keep the water inside the head so you wouldn't have a super wet spot around your lowest point head. Hunter claims this also prolongs the life of the head.+Stainless steel riser option if you pay more - protect against sand and people. In sandy areas your plastic riser would eventually fail (scratch by sand/dirt) and wouldn't go down when the water is shut off. It's also useful in heavy traffic areas when people accidently bump into sprinkler heads.To me, the I-20 and its stainless steel version are well worth the money.The equivalent of I-20 for Rainbird is 5500 series. I have hands-on experience with 5000 heads but not 5500. After reading the manual, it looks like the drawback of 5500 is that it doesn't have a FloStop Control, while the advantage is it lets you adjust both left edge and right edge easily. On the I-20, the right edge is fixed, thus to adjust it afterwards requires a little bit more effort than the 5500. To me, I'd rather have the FloStop. By looking at Rainbird's website, it looks like 5500 offers less nozzle options than Hunter I-20.[...]