OpenAPS is not an algorythm. It is a set of tools that allows you to communicate with a few different medtronic pumps (so far, more coming) as well as medtronic and dexcom cgm's.
Openaps allows those communications with the pump to happen using several different devices including things like a rileylink, carelink stick, TI stick and others. Openaps can be run several different ways on different hardware including raspberrypi, intel edison, ios, laptops, etc.
There are a few different algorythms that compute temp basals. One of them is oref0, which is what many people use on linux based devices. Another is openaps-predict which also runs on linux setups and has also been adapted as part of Loop for the iPhone. There are a couple other algos that a few people used but are more privately built.
The two algos are different in some ways. Both are open to user edit to make their own and add bells/whistles and add/edit constraints. Both encourage people to make them your own.
I have used both for approx 3 months each. Both are good. Both required me to learn and adapt and fine tune my settings (insulin action duration, carb ratios, target rates, etc). Both are aggressive if you want them to be and both are conservative if you want that too.
My personal take is that oref0 worked slightly better for me. I think it was mostly due to advanced meal assist which has a means to detect when you are resistant for some reason and will become more aggressive.
I have used Loop/openaps-predict for the last 3mo and it has been working well too. It has some great features like exercise mode built in. It is very straightforward in how it calculates the basal adjustments. It displays what it predicts your bg to be over the next 3 hours which is very useful.
I think if you are considering an OpenAPS based solution you should look at both. Both algos and what platform makes the most sense for you. Hopefully soon we will have multiple algo choices for the iOS platform like we do with Linux.