well i can only advise my personal experience this year-----basically promised to get back to me--never did--awful!!.....but i add it is only my experience
This is my third year booking with bulgariaski and have
had no problems with them at all,always book a few nights in Sofia first.At the moment organising a days skiing up in vitosha.transfers are good,with english speaking drivers.Borovets rep 'vladi'is a great help and his wife is nice too.Great company to deal with!
We booked with them when we went to Borovets in March this year.
We had no big problems. The only thing is they sometimes take a little while to reply to emails but other than that no problems and Vladi is Fantastic!!! So helpful and really lovely.