Can't comment on the differences. But I would say it doesn't matter which one you do in a placement year. Just do it enthusiastically.
Wherever you end up, you should try and get as much insight as possible in to the other areas of business. After a few months try and get introductions to people around the business. Most people will be happy to spend some time explaining the work they do - even if you have to approach them cold.
Do it tactfully though and make sure you always look committed to your current business area. Partners can be sensitive! After all, chances are that's the area you'll want a job in after uni anyway.