There are a variety of Biochemistry books on the market, and Stryer and Voet are certainly the front runners. Stryer is a smaller volume with a less chemical focus, whereas the Voets often get very deep into their subject. So, if Biochemistry is something you have to do as part of a course, you're likely to find Stryer clearer and quicker to learn from: but if like me you love Biochem, you'll love Donald and Judith! It's a fantastic book, in my opinion the best, and certainly an argument settler. Let's hope for a new edition soon.
C'mon - if you're serious about biochemistry you need this book. For me, it could only have been improved with some stereo images on the printed page and a DVD insert for IT extras to enhance the content - we are in the 21st Century, after all.
That aside.. this is a book and it's excellent. I would recommend you get this for your A level student considering a pathway into biochemistry. Just referencing this through their A level studies will bring the whole subject alive for them and, hopefully, inspire rather than scare them when they see how much more there is to find out.