Spotting in the Balkan

[michel N]

Good morning,

I will be going to the Balkan for a weekend, for the airforce days in Serbia. I have got some time left, so I want to visit one of the next airports:
Sofia, Bulgaria, or
Podgorica, Montenegro or
Petrovec in Macedonia.

Has anyone got experience with these (military part of) airports? If so, where is the biggest chance of seeing anything military?

thanks in advance!

Michel