I'd strongly recommend Latin! I'm doing it now, and I'm loving it far, far more than GCSE, which was a little to easy for me, while A Level is a delightful challenge. The new grammar is relishing, filling in the gaps of verb tenses and the such, which means you get to study Latin from original authors (though slightly adapted) as opposed to modern passages, which is much more entertaining, but then it's not too big a step up. While the lack of a defined vocab list for the full A Level is almost worrying, you are given the obscure words in the exam like before, and you build up a store of new words from reading the authors from which the unseens are taken (the spec will tell you that, for OCR it's Livy and Ovid) in Latin, which is thrilling, to read literature in another language. The literature itself for the set texts is indeed harder, and they are individually longer, and there are 4 to learn (provided you don't take the AS, in which case it is half that), but they are, at least for me, far, far more entertaining than the god awful Pliny I had to deal with at GCSE (damn Pliny the Elder's daily life! it's dull!). Aside from the superiority of the A Level to the GCSE, it's quite a unique qualification to possess, which attracts the attention of universities and employers alike.