This is a really common post on this site. You might read down some of the recent posts on this topic.
A few years back, I threw together a list of some commonly kept snakes and tried to rank them objectively based on criterea that might be important to the inexperienced keeper (by inexperienced, I mean in regard to number of species rather than just amount of time).
I scored each species on several variables, such as adult size, temperament, cost of housing, cost of feeding, cost to purchase the original animal, and availability as captive born.
It is woefully inadequate in number of ways, but here it is to maybe give you some ideas. The ones towards the top of the list scored highest as good beginner snakes. The ones on the bottom aren't good choices for a variety of reasons.

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Chris Harrison
San Antonio, Texas