I was in the same position as you. I did 'The Golden Age' and 'Extinction' last year. I put all my energy into studying Extinction, but I honestly couldn't bare it and decided to switch to TGA 6 days before the final exam (lol). Extinction was emphasised to be studied for the text response (it was for our SAC 1) and TGA was only for our creative SAC.
Honestly, I didn't even read the book for TGA at all and just read the synopsis online + learnt the themes of it, and it worked wonders because the essay prompts weren't too difficult (suss out the 2018 and 2019's prompts, they are definitely not rigorous). What made this book quite easy to analyse was because it was (relatively) relatable, so it's quite easy to draw up something, if that makes sense.
Nothing wrong with Extinction at all, but I personally hated it and found it so mind-numbing hahaha. It's up to you though.
ETA: didn't read properly that you wanted a short text, so in that case Extinction is probably a good option (as mentioned before, it is a short play). For TGA tho I still believe it's an easy text to analyse and draw stories from (I also memorised my intro and a few paragraphs and it still flowed LOL) , but if you don't want to cut corners then extinction is good