Would you say this was normal?

[Admittedly]

I have one child with DH and two step children (9 & 12) My DC is just a baby (nearly a year old).

One of my step children absolutely dotes on baby, like is obsessed with them, plays with them, helps them, helps us with them.

The other couldn't really care less. Which I honestly don't expect them to, I don't expect them to play or really care. They are nice to them but just aren't really interested which is fine.

But quite honestly I prefer my step child who loves our baby so much more because of how they are with them. I feel so much more for this DSC and prefer spending time and effort with them much more than the other and I am aware that this is because I see how great they are with my child.

Normal?

Which is the bit you are asking about normality on? Some kids are interested in babies, some aren't, which is completely normal. You are going to bond more with the child who is attentive of your baby, which is also normal. Just make sure your DH makes sure the other child doesn't become excluded.

It having such an impact on my preference of them both.

It's not unreasonable to prefer a person (of any age and with any relationship to you) who makes an effort with your child vs someone who doesn't. It's perfectly normal

I don’t think it’s unusual for children of those ages to be disinterested in a baby. Babies don’t do much of anything for long at that age. But if they were totally disinterested in a 3 yo I’d be more surprised.

And of course they should be kind, even if they’re not interested.

I’d say park up how you feel about this now and revisit in a couple of years.

I prefer my DSC who treats LO like a member of the family to the one who treats them like a toy to play with and keep them entertained, and an inconvenience when LO gets in the way or needs attention. The one who doesn't really make a fuss also doesn't get board and ignore LO.

Even in intact families, it is not unusual for young children to have varying responses to a new sibling. Some may be more interested or engaged with the new baby others may find them to be of little or no interests. That typically changes as the new born becomes more interesting and capable of engaging with older siblings.

Parents typically do not let the level of engagement with the new born govern their interests in their older children. This may or may not be the case for all or even most step parents.

It would be very wrong for your husband to feel this way, but for you not so much.