If they're good tenants, I want them on a year lease to keep good cash flow for longer. I often offer incentives for this (i.e. no rent increase if they sign a new lease, or even re-signing incentives, depending on the circumstance).
I will only go M2M if they won't sign a year, because I'd rather keep them as long as possible to minimize turnover and other expenses. (And I'd had tenants who went month to month stay for a LONG time--and even sign year leases later.)
If they aren't, I ask them to move out.
But all of my rentals are straight up investments. If you think you might need to move in, realistically, then it might be a different scenario. I'd still probably try to keep them though, if it's unlikely, and then if it does happen just look for a place to rent yourself short term, until their lease is up.