This is the most common planning question we get, and it's also the one that has the most impact on your trip. Where you stay on the south coast changes everything: what you can do each day, what you spend, how relaxed or rushed you feel, and whether you leave wanting to come back.
Here is the short answer, and then the longer one.
If you have five to seven days and it's your first time on the south coast, stay in Weligama. It sits in the middle of the coast, the beach is good, the food scene is the best value of any town down south, and you can reach Galle, Mirissa, Ahangama, and Hiriketiya all in under 45 minutes. You will not feel like you are missing anything by being based here.
If you have more time and want to slow down, split it. Three or four nights in Weligama, then move to Hiriketiya for the last few days. Hiriketiya is a small horseshoe bay with no agenda. The surf is consistent, the cafes are genuinely good, and you will decompress properly. This split works well for two-week trips.
If you are coming primarily for whale watching, stay in Mirissa for one or two nights during the season, which runs roughly from November through April. Whale watching boats leave at 6am, so you want to be close to the harbour. After the tour, move on. Mirissa's beachfront has become repetitive and overpriced, and there is no reason to spend a full week there.
If Galle is the reason you came, and it is a good enough reason, stay inside or very close to the fort. The fort is a different experience in the early morning and late evening when the day-trippers are gone. Staying inside it puts you inside that atmosphere. There are guesthouses in the fort at various price points, and even the budget options tend to be in interesting old buildings.
If you want quiet and you are not a first-time traveller to Sri Lanka, look at Ahangama. It sits between Galle and Weligama, it has a strong local character, good cafes and restaurants, access to the Kabalana surf break, and it has not been overrun. Dickwella, further east toward Tangalle, is another option at the quieter end of the coast.
One thing most guides do not say clearly: do not try to see the whole coast in one trip by moving every day. Galle, Unawatuna, Weligama, Mirissa, Ahangama, Hiriketiya, Dickwella, Tangalle. That is seven places in what might be ten days. You will spend most of your time in transit, live out of a bag, and feel exhausted. Pick a base, do day trips from it, and save the rest for the next visit.
We ask everyone who comes to us for an itinerary where they want to feel by the end of the trip. Energised, relaxed, or somewhere in between. The answer to that question determines where you should stay more than anything else.