My DD1 is 6 and in P1 at Dover. She's been there since nursery and loves it. It's not super-shiny like UWC and Tanglin with climbing walls, theatres and kayaking pools but it has a decent 25m pool (everyone swims every week), sports field, running track etc. The teachers are lovely, very nurturing and kind. Parents are more involved than my friends seem to be with their kids at UWC and Tanglin. We have lots of assemblies and celebrate all festivals. The headmistress is lovely and welcomes all the children by name every morning when the buses arrive. There is a special needs stream and full-time occupational therapists etc. We probably won't be requiring special needs help but I love the fact that DD1 knows the basics of sign language and is aware that people come in all shapes, sizes and abilities. Special needs children are taught separately but fully integrated when it comes to sports, special events, school trips and productions.
However, I'm not convinced of academic standards in the senior school and feel that there are better options out there (although Dover is currently investing lots in a senior teaching block they don't have the music / sports / drama / home economics / arts facilities of other schools).
We have signed DCs up to UWC - DD1 who is 6 should be there by the time she is 10 and DD2 who is 2 should be there by 5.
Tanglin accepts huge financial contributions to "jump" the waiting list, UWC does not. I know companies that have paid Tanglin's extortionate bribes jump-the-queue fees - if you're negotiating a package, would this be an option?
Just be aware that they all have slightly different school holidays which can be a PITA if you are planning half term trips or a long summer back home.
Heard good things about all the other schools you mention and have friends with kids at Tanglin and UWC so if you have any other questions, fire away.