Suggestions on a used Class C for a family of 4

Most important consideration is leakage. But go for biggest unit you can. It's a lot easier to say "I'm glad we got the 30 footer" rather than "This MH is too small." We got our first class c June last year, a 28', and in November traded it for a 32'. The 28' was too small for just wife and I. Heard once go larger than you think you need, you won't regret it.