Should I use /etc/bind/zones/ or /var/cache/bind/

Each tutorial seems to have a different opinion on this. For my ISC BIND zones, should I use /etc/bind/zones/ or /var/cache/bind/? In the last install, I used /var/cache/bind/ but only because I was guided to do so; however I just spotted a pid file in there for this new Debian install, so I figured that using the "working directory" to store zone files probably wasn't the best idea. It seems that many admins use this so they don't have to type the full path when declaring a new zone.

For example:

file "/etc/bind/zones/db.foobar.com";

Instead of:

file "db.foobar.com";

Is obviously easier to type, but is it good or bad practice?

Some may also suggest setting the working directory to /etc/bind/zones:

options {
    // directory "/var/cache/bind";
    directory "/etc/bind/zones";
}

… but something tells me this isn't good practice, since the pid file would be created there I assume (unless it's just in /var/cache/bind by coincidence).

I took a look at the manpage but it didn't seem to say what the directory option was for, any ideas exactly what it was design for?