All those areas are on the South East coast area with quite a long spread between them. Valencia to Murcia over 200 km.
Perhaps it may be best to book somewhere for a couple of weeks and look around. Perhaps base yourself in the middle (somewhere around Torrevieja) and there are good motorway links between the other places. Really, you need to decide what you actually want. Valencia is a big city which runs just like a city, Alicante not so big but still a city with all the businesses. Torrevieja (the poorest city in Spain, by the way) spread out and often includes the Orihuela Costa and has a population of around 100,000 rising to over half a million in the summer. Murcia is inland but has lots of coastal towns where people buy.
Some of the places can be ghost towns in the off season but packed to the gunwhales during July to September. Many of the areas you mention have lots of British (and other nationalities) living there which is no bad thing if you want to make friends.
There's also price. Valencia and environs are quite expensive as is Alicante itself. Guardamar through Torrevieja to Murcia are very cheap at the moment.
In fact, scrub my couple of weeks. Take a few holidays at a couple of weeks at a time. Also visit the Costa del Sol and look around. Whatever you do, don't rush in. We have had 3 properties in some of the areas you talk about. Whilst liking everyone of them, the first two were great for holidays but not for permanent living and we took over 6 years to find the area we finally finished up in. Quite a costly exercise when we take into account the falling property prices but ever increasing taxes (transfer tax for resale properties in the areas you mention is now 10% plus at least 2 or 3 percent more for legal fees - IVA (VAT) on new properties is the same). Best to look around a lot until you find what you want.
Best of luck in whatever you decide.