Get something that appeals to you. 50g is plenty big for most colubrids and small boids, so you have a lot of choices. In the kingsnake/milksnake family there are TONS of great choices. Some of my favorites: Honduran milksnakes, grey-banded kingsnakes and Mexican black kingsnakes. All can be easily handled if you handle them regularily when young. Bullsnakes are wonderfull snakes, but if you end up with a big one, 50g might be a bit tight. They can get to 7' or more. I've never kept gopher snakes, but I've read that Sonorans stay smaller...typically 5' or so. That would work out nicely in a 50g.
If you prefer boids (less active, heavier bodied), Ball Python, spotted/children's python, small boa constrictor (male Hogg Island for example), Jungle or Irian Jaya carpet python.
1 adult bull snake: "Dozer"; 1.1 juvenile bull snakes: Oscar and Phoebe; 3 baby red-sided garters; 1.1 macklot's pythons