Best universities in Bulgaria

It depends on what you want to study.  In my view, some of the universities here, especially in Sofia, are good, for example:

Sofia University St Kliment Ohridski - depending on what subjects you want to study (it's not the best for many technical subjects, despite what they might like to tell prospective students).

Technical University Sofia (TU-S) is very good for the subjects that it covers, which are actually pretty wide-ranging.

The others - no names, no pack drill - range from adequate (some barely so) to mediocre, or worse, again in my personal opinion FWIW.

That said, the vast majority of the foreign students coming here - with the exception of many of those under the Erasmus scheme - are also mediocre and tend to choose a university here because they can't make the grade for entry into a university in their own country and/or can't afford the fees that are charged in other European and Western countries.