Corns really are the best beginner snake, it is unlikely that they will actually reach 6 ft but it is possible. However you need to understand that they are colubrids... meaning they are pretty slender and easy to handle animals regardless of length (in this case) a 6ft corn is still easier to handle than a 3ft ball python. also, because they are slender they never appear as long as they are.
dekays aren't really great beginner snakes because their diet makes them difficult to keep in captivity.
pueblan milks can be you just need to expect to have a scared baby snake that will musk all over you and be ready to work with that to get it tamed down. Cali kings would also work well, they tend to be more nippy as babies and less musky.... at least that's what I hear... none of mine where ever nippy or musky or anything like that
Sand boas are decent beginners to my knowledge, sometimes they can be nippy and problems feeders, but not as problematic as ball pythons -.-
A western hognose snake might be another consideration. They stay very small and relatively easy to care for, most readily take rodents or convert rather easily (unlike easterns) however they are technically rear fanged venomous and though their venom wont kill you it can give you a bad day. That being said...bites are rare and easy to avoid when they do happen...these snakes have numerous defense tactics that come into play before biting..... i would imagine most bites are actually from careless feeding and the easy way to avoid that is to use feeding tongs....