I have not personally used the Ortovox S1, but in talking with people who have used it, it has a lot slower processor than the other beacons and takes a little extra time to "map out" the area.
The BCA Tracker has been a great beacon for a long time, it is a digital beacon with a fast processor and has two antennae. For a single burial, I like a BCA tracker as well as any other beacon.
The pieps and pulse are both digital and have three antennae. For multiple burials, I would recommend one of these beacons. They make searching for multiple beacons much easier and the three antennae eliminate the dead spots that occur sometimes with two antennae.
Whatever you do, get a digital beacon and PRACTICE