I keep Gophersnakes- closely related. If raised from young, and handled semi-regularly or regularly,
most will calm down pretty good.
They are neat snakes in my opinion. If you get one, you may think about starting them on rats from a young age, because waiting until when they grow out of mice may be a challenge. Of course you could just feed a few large mice per feeding. My 5 foot female eats a 100-120 gram rat per feeding.
A good fiesty wild caught adult is good to learn snake handling with though- you definitely will find out what handling moves make snakes feel threatened, and which ones do not- though I wouldnt recommend a w.c. adult be kept for a pet, as they will often be a challenge to feed and handle.
As far as what would be better? Get a pair of each!

I think the pine would be prettier, but they both would be good captives if captive born and handled from young ages.Some of the rarer pine localities are pricey, but very beautiful. The great plains rat snake would be much like a grey colored cornsnake from what I understand(closely related), not to say they arent pretty too.