Pros and Cons of Two Year Plus contract with tenant?

Tenancy Types and Management

Any thoughts please on signing tenants up for min 2 year contract. According to my letting agency a Family wants a 3 year contract but after my last experience with rotten tenant I am not keen on signing up without a break clause after one year. I am getting the feeling my agent is trying to push for long term contract also (was fairly explicit that I wanted clauses). I can understand why tenants with families are keen to sign up long term but conversely if they are not happy a break clause would be of benefit to them surely. Pitfalls/pros/cons/ advice anyone how to approach please. Im wary of agent also doing their own thing in this. Gut feeling. Many Thanks