I definitely recommend a BI. I just got my first a couple weeks ago and she already has the most wonderful temperament. Definitely the calmest, least fearful, and easiest to handle of any of my snakes upon arrival. My other two snakes (blood python and KSB) are also wonderful, but they definitely took a little more work to get them comfortable with handling.
Blood pythons/other STPs are great and, in my opinion, underrated. You get the girth of a giant constrictor in a totally manageable length! Plus they’re beautiful. And despite their nasty reputation, if they’re well-socialized as babies, they can be wonderful to handle. Granted, I only have one, so my sample size is small, but she’s a doll. So personable and inquisitive. She was a bit nervous and hissy/strikey as a baby, but she calmed down after just a few handling sessions and has grown into a very sweet subadult.
The small boa species, like sand boas and rosy boas, are great. Small adult size, so they don’t require much space, very hardy, great eaters, and have beautiful colours. I love my sand boa. My girl is a large middle-aged female, and she’s not even 3’, so they’re a great species if you’re looking for something on the smaller side. I don’t have a rosy, but I love the look of them, and it seems like the people who have them really enjoy them (though they seem more likely to try to eat you than a sand boa 
).
House snakes are another great smaller species. I’d love to have one some day. I’ve heard people compare them to tiny retics in terms of temperament and intelligence.
Hognose snakes are adorable. Hard to go wrong with those little drama queens.
If you like cresties, you might also look into Chahoua and/or gargoyle geckos. As I understand it, their care is very similar to cresties and they’re similar in size. If you want something bigger, you could look into Leachies. I love those guys.
Cave geckos are beautiful, though I don’t know that much about their care.
