Rob Andriessen wrote: it would be great to learn which regions of Bulgaria are the most interesting in the eyes of herpers with experience in the country.
This depends on what are you most keen to see. All regions can offer nice findings - for berus, zootoca, coronella, anguis I'd try western and north-western parts of the country and high mountain regions like Vitosha, Rila or Pirin mountains (although the latter also has Platyceps, tortoises, P.erhardii, R.graeca and more). For more "southern/mediterranean" species (etc. Malpolon, Eryx, Typhlos, Ophisops, Pseudopus, Mauremys also Platyceps and tortoises) I'd stick to Kresna gorge, Eastern Rhodopi Mountains, Strandzha Mountains and the southern Black Sea coast. L. viridis, Natrix, Emys, Pelophylax and ammodytes are practiclly found throughout the country so you have a chance of seeing those wherever you are.
Rob Andriessen wrote:we also want to include areas with great scenery, and, if possible, bears
I think you won't have a problem with nice scenery
I can't say the same for bears though. You can get them throughout the country but their stronghold is the Western Rhodopi Mountains. In any case it would be hard to find any.