We're in the same boat, and not sure what to do. DD is young in the year, not 3 til August, and has been doing a few hours a week at her private nursery since January. Settled really well, loves it, no problems. She has a place at the nursery in the primary school where we intend to send her, and until recently the plan was always for her to stay where she until September, then switch to the school nursery. But starting to wonder if she will be ready. The current nursery has a preschool room, for children turning 4 that academic year, and the free hours are available there. Both settings are nice. The nursery is rated outstanding, the school good, though I don't know how much attention to pay to Ofsted anyway. I just wonder if she's ready.
In our case, the hours are a point against the school nursery, because it's 9 til 3.15. That seems a ridiculously long day for a child barely 3. They've said we can do a phased start, but not many kids do this after the first few weeks. I'm wondering if it would be better, if we don't want her FT for a while, to send her to an actual PT setting rather than PT hours in a place that designs the programme for 30 hours. On the other hand, the private nursery can't do the hours we want either- prefer 3 x 5 hour days, but they can only offer than from 8am which won't work well for us. So we'd have to take the 15 hours as two 7.5 hour days, and not send her for all of it, then pay for a shorter session on another day. I'm not sure what the work situation for me is going to be in a few months either (on ML with no job to go back to...) so it's impossible to plan!
But basically, it seems to be a choice between a setting that will better prepare her for school, and one that's more specifically designed for younger children, iyswim. The school nursery seems a lot more structured, but then it might be a bigger leap between nursery and school if she stays where she is? Torn!