I made a few comments about Montenegro in your other thread, but they weren't town-specific, so these are my thoughts after a one-week visit in 2015:
Kotor: Very picturesque medieval walled town. You can walk on the wall. James E has called it a sort of mini-Dubrovnik, and upon reflection I think he may be right, though the historic district is far from small. It does get some large cruise ships, so the trick will be to check online cruise-port schedules and try to avoid days when monster ships are due in. On the schedule I've linked, you can click on the ship name to find out its passenger capacity.
The trip by bus around Kotor Bay is lovely. There are also some boat trips. Works as a base for Budva and Herceg-Novi as well as for boat trips on the Bay of Kotor. Might work for a day-trip to Cetinje, but another poster has warned that approaching Cetinje from Kotor takes you along a hair-raising road.
Budva: Somewhat similar to Kotor in appearance, but not as spectacular. The old town is a healthy walk from the bus station. Like Kotor, quite touristy, though I don't think it gets large cruise ships.
Herceg-Novi: Another atmospheric coastal town north of Kotor. Being more different from the latter, I'd make it a higher priority than Budva, but others might disagree.
Ulcinj: Coastal town to the south (near Albania) that is very Turkish in feeling. Recommended. Comparatively few tourists. Bus station quite a walk from the old town.
Cetinje: Historic capital, very pretty and--as an inland town--with an appearance quite different from Kotor and Budva. Doesn't get many tourists.
Podgorica: Definitely a smaller percentage of attractive buildings than you'll encounter in the other cities I've listed. A good bit of ticky-tacky Titoesque architecture, and my general reaction to the city was to call it "charmless". However, I wouldn't be surprised to find that it has a worthwhile museum or two, and I hardly gave the city a chance since I just used it as a base for day-trips to Ulcinj and Cetinje.
Lake Skadar: Good for bird-lovers. You can actually get to the lake by bus, then you need to pay for a boat ride. Not so easy to arrange before you get there unless you take a tour, but I found someone to take me out on the lake for 25 euros. I don't remember how long the trip was--maybe an hour.
Lovcen National Park: Difficult if not impossible without a car unless you can pick up a bus tour somewhere. Said to be really lovely.
Beyond Podgorica, as you move toward the Serbian border there's some lovely country. A guide book would help you out there, but I'm not sure about the frequency or extent of bus service east of Podgorica.
It's possible that it would be affordable to hire a car and driver (taxi?) for a day or two. It's a small country, so distances would not be great.