I loved Chemistry, so may be a bit biased...
Anyway, I'd say that Chemistry would be really useful in terms of keeping lots of degree options open - e.g. many science degrees (including some of the more biological sciences) like you to have chemistry, and it would be really useful
Also, quite a few universities only require one language to be able to study languages at university (e.g. a pure Spanish degree, or Spanish with another language ab initio).
Mind you, you've also got to enjoy your A level subjects - you'll be spending a lot more time on each than you did at GCSE, and enjoying them will really motivate you to get top grades
Have you considered taking five AS levels? You could do it just for the first month or so of sixth form to figure out which subjects you prefer more, and if you find the workload manageable could stick with all of them until the end of the year...
Also, not to complicate things even further but for engineering Further Maths would be super useful - many of the top universities will expect you to take Further Maths for engineering courses, and even for universities that don't it would make the first year of the degree much easier.