Leases are up.

[Mara Witt]

I own a duplex, both sides have been rented to good tenants for the past year.  unit A is a single woman and her teenage daughter, I'm pretty sure she will be a long term tenant.  Unit B is two twentysomthing guys, roommates. Both sides have been good tenants and I'd like to keep them. So, now that leases are up should I draw up a new lease, or let it just go month to month?