I for one would not vote for any member of the Pituophis family- Gopher snakes and Bullsnakes can be rather aggressive, they are also a deal larger than cornsnakes.
I have a Texas Ratsnake... there's no avoiding it- at the very early ages he was very aggressive and I had to calm him down over time. Sure it's a nice experience but you run the chance of them staying that way... and that's no big fun for anyone.
Milksnakes... dunno, not my taste... out of the Lampropeltis I would recommend any member of the Mexicana complex. I think they are insanely beautiful, as docile as snakes come, and loads of fun. Yes, breeding can be a chore, and getting the babies to feed if you breed them is rather difficult and takes a lot of time. But on the brighter side, they are very versatile without having to dig up morphs- especially the Thayeri's. They are a tad smaller than cornsnakes, when they mature they need one large mouse a week and all in all, don't take neither room nor a lot of resources to keep.
BP's... those are nice, sure. But I find them kind of boring. Few snakes can look so adorable... but let's face the facts... as they mature they hardly move, they hide and are far less interesting than a cornsnake. The morphs are great, but very expansive.
Out of the colubrids I decided to focus on the Mexicana complex. Out of the rest... I chose BCI's. I have access to BCI's whose parentage dates to the Hogg Isle population- meaning that they are rather small in size. The father of my Boa, after 2 successful breeding seasons is only 5 feet long.
A 5 year old female got around to 5.5 feet. - Basically, it's a travel sized Boa, hehe. All I can say is that BCI's are very impressive, very docile mostly and... I really can't explain what is it about their aura but they are extremely impressive where I think Colubrids can be very comic(in a good way!).
If I could, I would get my hands on a couple of Thayeri's and see the magic they create with each breeding. But that's just me