I have a pretty low opinion of BitLocker. It's better than it used to be but it was never great.

PGP Whole Disk was a very good product years ago, and I've heard that it is still pretty good. But it's expensive.

I really do not know what to recommend. Last week I would have told you to use TrueCrypt. I'm thinking I'm going to wait to see what Bruce Schneier says about this. There are some good comments on his blog: https://www.schneier.com/blog/archives/2014/05/truecrypt_wtf.html.