Have you ever lived in a different (assumption that you’re British, sorry if you’re not) country besides CTC? If not, and you think you can make the finances work even at a stretch, I’d take the Spanish base. You’ll more or less always be able to get back to gatwick (obviously this is a bit brexit dependent) and it is a really enjoyable experience operating from a smaller base. I started in a French base before moving to LGW, and wouldn’t have changed it for anything. Yes, moving country was a bit daunting. Yes, attempting to do anything formal like bank accounts etc was a bit of a nightmare, but there’ll be people in base who will likely offer to help if you ask for it.
Starting in a small base is is a fantastic way to enter the industry - you’ll get to know the people you fly with and this will help your learning at the early stages. When all is said and done if you decide you don’t like it, you can leave and take it as a good experience.