If married, is it better to submit a separate or joint (with spouse) tax return

Yes it is, no it is not

It all depends on the reasons not to want to file together.

You could work them out both ways and see which way is best

So can you file one year as joint and the next as separate?

You may file married filing separate or you may file jointly.
Your status can change because of obligations of the other partner, wages of both and more.
It is more common to get higher refunds when filing jointly,
Is there a reason you are considering, married filing separate