This may be a bit dated, but I'll be going to iOS whenever I drop my Lumia; specifically, an iPhone 7+.
iOS 12 will run on the 7+, it has a decent CPU, and I can find one for a reasonable price. A client who used to be exclusively W10 whose company does CRM development on the cloud using Azure based architecture among others switched to iOS after finally losing patience with MS and seems very happy with the change.
I'm not sure about Android because I don't trust Google (even less than Apple) and there seem to be too many subsets of the distros depending on which carrier/manufacturer you're dealing with.