Well you are choosing between
@RambleAmple ’s third A level choice (psychology) and mine! Your third A level choice doesn’t really matter so I wanted to make it my fun choice that I enjoyed the most. I was in a similar position to you, I was stuck between geography and Spanish. I started with the former and hated it, but my school let me switch just before October half term and I managed to catch up just fine! I loved Spanish and for me the lessons split my sciencey subjects up nicely.
A Level Spanish is quite different to GCSE. You’re no longer rote learning vocabulary about where you go on holiday and your hobbies. The A Level is essentially learning Spanish history (such as Franco’s regime), Spanish and Hispanic culture, and sociology/human geography all in Spanish.
Then, you have a book/play and film that you study and have two essay questions. The writing paper also has a translation into Spanish. The reading is similar to GCSE just harder with a translation into English. Also, for the speaking exam you discuss a topic of your choice that you have researched - I did the biodiversity of Costa Rica which was fun to learn about. In regards to the listening exam, the nice thing about the A Level is that you can pause and rewind the clip which really helps.
Obviously all that was for my exam board, the A Level is roughly similar for all the exam boards but definitely find out which ones your school uses and look up the specifications. You say you’re not big on longer answer questions which Spanish does involve in the reading and writing papers as well as in class as you’ll be doing plenty of practice essays and translations.
What I’d be concerned about is your current level of fluency as the GCSE and A Level isn’t really designed for people who already speak it at home etc, what grade are you currently working at?
Edit: I must mention that at least when I did them, A Level languages are known to be hard to get an A* in - I’m talking 85%+ which is madness for a language, not to put you off or anything but it’s so normal to be stuck on lower grades when you start off with it