I think I'll go with a smaller operation, I don't want to be the new guy out of 40 if I can be the new guy out of 4.
Actually, you do want to be the new guy out of 40 and not the new guy out of 4.
In general, the bigger operators in resort areas tend to attract the newer divers, and they will be well able to handle them. They do it every day. In a group of 40 in Aruba, believe me, you will not be the only diver with only a little experience.
In contrast, the small operators frequently tend to attract the better divers. If you are the only new diver out of 4 with a one boat operator, and everyone else is highly experienced and looking for a challenging dive, neither you nor they will be happy.
Of all the places I have dived, Aruba is where that is most true. When I was there, I went with the smallest operator possible, Dive Aruba with Clive Paula. It is a one man, one boat show entirely. (I hope it is still open.) I really enjoyed myself with him, but I would not recommend him for a beginner. You are much better off with him if you have some pretty decent skills to begin with.
The bigger operators will have multiple boats, multiple dive masters, etc. They will be best able to give you a dive at your comfort level.