I'd say either mouse hoppers or mouse fuzzies, some boas are born very small and hoppers may be too big. I start all my boas on mice until they can take weaned rats, the mice are more fully formed and a boa can take a non-nursing rodent much quicker on mice vs rats. My boas are normally taking hoppers up until they're 9-11 months old, and then are on weaned rats by about 1.5-2 years old. From there, I might see one prey size increase per year, and then I stop at large rats. No jumbo mice, jumbo rats, pinky mice/rats, Guinea pigs, pigs, or hamsters, due to fat content. If my boas outgrow large rats, I either jump to 1 lb rabbits, or feed a jumbo every third feeding (so large-large then jumbo). My biggest is 7', so none of my boas are eating anything bigger than regular larges (150-275 grams) yet.

I also start my boas on 10-14 days from birth. The first 1-3 meals can be spaced out by 7 days, but I prefer to feed my boas a little less often. I have noticed similar growth in my boas fed half as often as other keeper's boas fed every 7 days (when fed similar-sized meals as I do).