I have worked in nurserys and also been a nanny. Im now about to become a childminder.
For babies and toddlers I would say nanny or childminder every time. Its much better for them to have a strong bond with one person. Also there is much more flexibility for getting out and about, rather than spending the majority of the day in one room.
Childminders are only allowed 1 child under the age of 12 months (although twins can be accepted too), or up to 3 children aged 1. In nurserys there can be many many babies in one room, yes the staff ratios are correct but it can be chaotic, noisy with lots of crying and its very difficult to meet each childs individual need. In one nursery i was told not to pick up crying babies as it would spoil them, which was horrible. I picked them up anyway but other staff werent happy about it! In my opinion babys and young toddlers need lots of attention and comfort, and they are more likely to get this in a nanny/childminder situation.
Some babies have a more sensitive personality than others. This type of baby especially shouldnt be in a busy nursery. So take your babies personality into consideration too. A very sociable, adaptable and boisterous type may do better in a nursery.
I would never put a baby in a nursery. However this is just my opinion. Go and visit as many settings as you can, and go multiple times so you get a proper feel for the place. Trust your gut.