I use 0db center, but if -3db center were the only option I'd be happy with that.
The 0db center means that things get 3db louder as you move them to the center from the sides, mimicking the natural behavior of stereo sound reproduction. I'm accustomed to that behavior, and it seems very natural to me. As I pan things out to the sides, I tend to turn them down anyway, since they become clearer as they move out of the congestion. This pan law just does it for me automatically.
Some folks find it disconcerting when the volume changes with panning, which is why the -3db option exists. If you do a lot of panning automation, it might be the better option. However, I find that pan envelopes need to be paired with volume envelopes anyway, making the pan law choice moot.
And of course unless you automate panning, it really very little difference which pan law you use.