I didn't have much snake experience when I got short tails, I'd had my ball pythons several years, added a hognose, then a SSTP (then a blood, then two borneos lol). The sumatran is the calmest of my short tails but I don't think you would have to start with one of those, you just need to be honest with yourself if you can handle a snappy baby, realizing they grow fast and be willing to work with it while young and small so you are comfortable handling. My female borneo is a dream, once you make clear you aren't food, but the male is a jumpy stressed out spazz, my blood is touchy in the cage but better once he's out.
There are chrome head or orange head sstp that do not get as dark and show more pattern, if you do decide on a sstp but don't want an all black snake. I am limited on space for snakes also so fairly picky on what I add too, I made a leap into short tails and another leap into boas with a 5.5' BC, sounds like we have similar taste! Not much chance to see or experience variety up here so just did my research like you are.