Not too familiar with rosy boas, I think their temperment and speed are between that of a bp and a king. Manageable size and may be a good happy medium. Would probably be a lovely first snake.
Kings are hardy, pretty, generally calm, not all that fast, and good eaters. However there's certainly a bite risk. Mostly from feeding errors and very strong feeding responses. But that varies from snake to snake. The majority are fine or manageable
Balls, are from what I understand, sweet tempered slugs with particularly cute faces. Very slow moving and docile, but be sure to buy a cb one from a reputable breeder. They require more heat and humidity than a king and have been known to drive beginners nuts by fasting but getting a cb one minimizes that problem.
Any of the three would be a very respectable first snake.
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0.1 chickens (Condor)
0.2 dog mutts (half ownership, only mine when they misbehave, Lucy & Amy)
0.1 Halflinger horse (Crissy)
0.1 Normal phase California Kingsnake (Sophia)
1.1 parents
Still searching for 1.0 WC human