Diazepam and clonazepam are the longest acting benzos, with up to 60 hours elimination half-life for diazepam, and up to 80 for clonazepam. Diazepam kicks in quite fast, clonazepam does not. The longest however seems to prazepam, with an elimination half-life of up to 200 hours.
As @SleepyTime explained, you can find their characteristics on the internet.