Weligama and Ahangama are 15 minutes apart and sit on either side of the centre of the south coast. They share a similar local atmosphere but attract different types of travellers, and the right choice between them is genuinely worth thinking about.
Choose Weligama if it is your first time on the coast, if you are learning to surf, or if you want the most practical base for exploring in both directions. The bay is long and calm, the beginner surf is the best on the coast, the food scene is strong, and the transport connections are excellent. Weligama is central enough that Galle, Ahangama, Mirissa, and Hiriketiya are all easy day trips. It is the base that suits the most travellers for the most types of trip.
Choose Ahangama if you are an intermediate or more experienced surfer, if you have already done Weligama on a previous visit, or if you prefer a slightly quieter and more local atmosphere. The surf breaks at Kabalana are a meaningful step up from Weligama's beach break: The Rock is one of the best A-frame reef breaks in the country for intermediate and advanced surfers, and Marshmallows provides longer, more forgiving rides for those building their reef surfing. The cafe scene in Ahangama is arguably the best on the coast, with a higher concentration of genuinely good coffee shops and restaurants per square metre than anywhere else between Galle and Mirissa. Evenings are quieter than Weligama.
What Ahangama does not have is Weligama's range of accommodation, its level of beginner surf infrastructure, or the social atmosphere that comes from a larger volume of travellers passing through. If you want to meet other travellers easily, Weligama is the better base for it.
The practical combination that works well is two to three nights in Weligama followed by two to three nights in Ahangama, or the reverse. They are close enough that you do not lose access to either when you move. Many surfers do exactly this: learn or practise at Weligama, then move to Ahangama when they are ready for reef breaks.