How do you split holidays with both sides of your family?

My husband and I grew up in different countries in families with different religions. No holiday overlap! Allocating vacation time to see everyone is still an issue though...

We alternate Thanksgiving and Christmas every year with my husband's and my family. Neither family is close to us so we are usually traveling for both. We have it synced up with my sister's family who is 3 hours away so we get to see them at whatever holiday we are celebrating with my family.