Is a 2 year labor warranty on a new roof long enough?

We had several estimates done to get a new roof on our house and the most knowledgeable. honest, nicest guy, and intermediately priced guy, had the shortest labor warranty of 2 years. Other places that were more expensive and also not as honest (said I needed to replace all my vents when they are practically brand new) had a 10 year labor warranty. The shingles have a 25 year warranty, so I'm wondering if these are appropriate warranty terms. What's the average labor warranty on a new roof? Thanks.