You can pretty much use any Linux or BSD UNIX you want. Most likely you will get familiar with the package manager for that platform.
If you use OS X, for instance, you might install Homebrew and install scientific packages made available via Homebrew Science, which is usually as easy as:
$ brew install homebrew/science/some_package
If a package isn't available, you can almost always compile it from source code via GCC under Linux, or Clang/LLVM under OS X (via Xcode).
It really doesn't matter. Linux distributions will often have samtools in their repo., so you don't need to compile it yourself (of course, that's simple). Of course if the Unix that you install is one of the BSDs then that's probably also the case for it (likewise with Mac OS X).
Linux is a Unix-Like operating system. There are many popular distributions based on Linux for example Red Hat, Fedora, openSUSE, Ubuntu, Linux Mint etc ...
For a personal computer i suggest you Ubuntu or Linux Mint.