My little one is 2yrs 3mths and we use both and have done since we started childcare.
at 9mths he started with a childminder 3 days a week and then he started nursery 1 day a week at 13mths ( i used a day a week annual leave for almost 4mths!).
At 2yrs we had planned to change to 2 days of each however at 18/19mths we changed cm as our one was due her baby and new childminder only had space on 2 days.
we now do tues/fri with cm and wed/thurs with nursery ideally cm would be 2 consecutive days but didnt have space and it all works fine.
He enjoys both and actually prefers childminder I think as gets more excited going there this has been since he went into the bigger room at nursery a few months ago not that he hates it just think its alot more noisy and busy for him.
I like that he has 2 very different environments with current cm (old one they were home quite alot and baby or no baby we prob would have been changing) they are out at playgroups/cm groups, school run, other activities if she has him on his own sometimes on a fri when other mindee is off they do something totally different which she couldnt always do with 2-3 toddlers (went to an art festival thing once where he did loads arts/crafts and they had lunch out etc). Nursery is lots children and gets him used to that busier environment as school isnt that long away really and he is an aug born child so will be the youngest when he starts school. I chose a montesorri nursery as its needs led rather than age led and they had a baby room (0-1ish) and baby/toddler (1-2ish) and a toddler (2-3ish) and pre-school (3+) room and he started in baby/toddler room and moved later than some of his peers to next room and they felt he wasnt ready for the hustle and bustle of the bigger room and when he did move he actually managed it very well which he wouldnt have done if he moved earlier.
I think there are pros and cons to both - can you cover if childminder is off sick/when she is on holiday? what happens over xmas - many (not all) nurseries close for a week can you cover it? (some childminders also have the week off but not all)
Our nursery costs us £16 more a day than childminder however nursery is 7.30-6 and cm is 7.30-4.30 (although pay til 5 in case running late never have been but its a daily charge for 8-6 so as I needed earlier this is what we agreed and works for us).