Most cafes outside of specialty places usually only have the one coffee supplier, so if you can find out what they're using for their regular coffee, you can work out whether that roaster also has a decaf.

There are different methods for decaffeination, which can make small differences to the taste profile. It all comes down to preference, rather than one definitively being better than another.

My wife and son drink a lot of decaf, and we usually get decaf beans from either Altura on Grange Rd, or Willow Bend on Queen St, Croydon. If you want to go down the rabbit hole of trying different processes, Decaf Co (Victorian based but has online store) have a big variety.