can't say much about the age, but we have used a nanny, a CM, and a nursery in the 20 months I've been back at work (since DS was 7 months). The reason for the mix and match approach was finding someone who had space -nursery had an 18 month waiting list when I registered DS there (at 5 months pg!), CM only had 2 days free, and our friends suggested a nanny share with their nanny, who they loved.
Nanny was atrocious - expensive, and ignored all my (perfectly reasonable) requests - such as feeding DS the lunch I provided, or giving him the bottle of milk I'd expressed, or giving him a nap. She lasted 3 months, whilst we struggled to find alternative care. I threw out a lot of breast milk too, which pissed me off hugely!
Childminder has been wonderful, and I can't praise her highly enough - DS adores her, loves her kids, and is good friends with one of the other toddlers she minds (and now we are becoming friends with his mum). She listens to my requests/concerns, and addresses them immediately. Despite not being a bfing mum herself (ever) and never having done it before, she fed DS expressed milk happily, and has really helped me so so much with any worries I have! She got an outstanding Ofsted report last year, and deserved every bit of it. All of us parents who use her love her!
Nursery have been good, but not as exceptional as CM. DS started at 12 months in the end. V supportive of bfing, and parents dropping by unannounced, very responsive to parents, in general the staff in the rooms are lovely. Management, not so great, and not good at communicating, but DS is happy there, and loves his days there. He adores his keyworker too, and I really like the room he's in now - the baby room was a bit too chaotic for me and DS, but as he's moved up the rooms, he has become a happier child. Not helped by him being an early walker, so in the baby room he was charging up and down, whilst the other babies rolled around a bit. They were also outstanding Ofsted last year, but IMO not as good as our CM! Moving rooms every few months is a bit disturbing for a small child too, although it seems to be settling down at our nursery - but they have rooms for babies, early toddlers, older toddlers, 2-3 yr olds, and pre-school, so by their very nature there is a lot of moving in the early years then more settled periods when the kids are older.
I have registered DD with CM and nursery for January - she's due in June :o btw, if you're due in June, feel free to join us on the June thread to whinge about being pg!!)
Sorry this is so long, but just wanted to say a bit about our experiences with all 3 kinds of care!! (I am aware that we were unlucky with the nanny too, so please don't think all/most nannies are that bad!)