The reason the corns look like a rat snake, is because they are a rat snake! The corn snake is in the same species as all the other rat snakes. Elaphe (or Pantherophis if you go by the new name).
As far as temperaments go, everyone says the corns are the most mellow, however, I think it is just in how you raise them. I have a few rat snakes (corn included) and they all are really mellow. I dont have a Texas rat, and I think they have a bum rap. I know quite a few people who have them, and they are no different than any of the other rats.
You will always have that one individual, no matter what species of snake, that is just the meanest S.O.B. But as a general rule of thumb, the rats are a very mellow snake and make good pets. Very hardy and quick to feed on F/T mice/rats.
All rats as hatchlings will be pretty squirmy, but calm down with regular handling.
I would say go ahead and get yourself a texas rat, but be warned, you will want another, and another, and.....
-----
1.0 Corn snake "Warpath" (KY locale)
1.0 Black rat snake "Havok" (KY locale)
1.1 Black rat snakes "Punisher and Mystique" (MO locale)
1.0 Eastern Yellow Belly racer "Nightcrawler" (MO locale)
1.0 Albino Black rat snake "Malakai" (Dwight Good stock)
1.0 Everglades rat snake "Deadpool" (Dwight Good stock)
0.1 Greenish rat snake "Rogue" (Dwight Good stock)
1.1 California king snake "Bandit and Moonstar" (Coastal phase)
1.0 Prairie king snake "Bishop" (KY locale)
0.1 Black king snake "Domino" (KY locale)
0.0.1 Eastern Milk snake "Cable" (KY locale)
0.0.1 Eastern/Red milk intergrade "Omega Red" (KY locale)
Good luck and Happy Herping
Brian