I don’t like any of them, though many of them have made some nice improvements.
RTG – forget it, though at least it’s the same across the software. Playtech is a bit clunky and I don’t trust the tracking, but the stats aren’t bad.
Microgamings – I think each of us should send an email to MGS, or through your favorite operator, asking them to standardize their backend so that we can get consistency and better stats without having to worry about what each program has to work out to please their affiliates – and then the aff programs can concentrate on marketing rather than programming.
Boss – useless.
Most useful (to me) – Brightshare, even if it is the simplest of programs, because I can freetag my affcodes and thus not have to go and register a campaign each time.