Been to all of them. They are all lovely. Podgorica is more of a modern city, while Mostar is a really, really beautiful city (especially the very popular bridge). I would definitely visit Sarajevo if I was on your place, the amount of tradition that city has, especially the very popular Bascarsija, is amazing. You've got to try some food specialities there, aswell. Budva and Kotor are pretty much same like Dubrovnik, but if you've never been there - it's just full of really interesting history, buildings and I am sure you'll enjoy it. Have fun visiting our Balkans!
Went Sarajevo with a few mates for a bit before. Loved the places and the locals were so friendly despite knowing very little English! Cheers for that mate, thinking of spending maybe 3-4 days in each place, that plenty of time? Will probably do hostels too as hotels are surprisingly quite expensive. Know anything of Albania? The country seems a bit of a mystery, which is intriguing.