Depending on the style of training, I would go with 1st the kennel club, or 2nd, the private trainer. I don't know if the citizenship test in your country is the same as here in the US, but here it's basically teaching the dog good public manners. Hopefully someone with more experience can explain it better, or you can do a Google search for "Canine Good Citizen Test".
I don't like the boarding for training option because I feel like the owner of the dog should be the one doing the training. Can you go to the kennel club and observe a class or two? That way you can get a feel for the teaching style to know if it aligns with your own philosophy of how you like your dog to be trained.
Niko: American Showline GSD 5 years old
Rosa: American Muppet Dog (GSD/Border Collie mix) 5 years old