....do you drive?
If you live on a mountain road and want to just have a blast driving 10/10THS with the tail hanging out and don't drive long distances cross-country, get the Miata.
If you drive on roads with faster sweeping turns and more long distance, get the Boxster.
Can't lose either way.
Oh, and if you DO travel, remember the Boxster has two trunks. You can pack more than a toothbrush.