I personally don't advise ANYONE to go to iOS. Apple products are overpriced and downright sub-par in terms of quality and the OS itself is absolutely terrible.
HOWEVER, that's ME. Now, for you I'll just ask these questions which will help you answer the question only you can answer:
1 - Do you prefer an open OS or a closed down OS?
Did you enjoy the fact that different brands couldn't touch Windows Phone's UI or way of working to improve it or change it?
If you enjoyed an OS that can't be messed with, then go with iOS. Much like Windows Phone, iOS does not allow you do change anything in it. Well, in fact, it goes further and only allows you to pick a wallpaper and rearrange icons (but not leave empty spaces in the grid).
However,
if you like to be able to customise your phone, including the ability to make the UI look like the UI of Windows Phone,
go with Android.
2 - Do you prefer to have a phone from the software creator or do you prefer to have options and pick the one with the features that most appeal to you?
If you want a vanilla experience just like the software maker intended it,
go with the iPhone. 'cause, you know, there's only Apple's iPhone on iOS, nothing else.
If you prefer options, then Android is the way to go. By the way, you can also get the "vanilla" experience on Android by either picking up a Google iPixel (basically Google's blatant rip off of the iPhone) or one of the new Nokia Android phones (which all come, unfortunately, with stock Android).
3 - Do you want to continue using Microsoft's ecosystem and have it integrated well with your phone?
If not, then go with iOS and enjoy Apple's integrated ecosystem. You can use Microsoft services there as well, they'll just not integrate with the iPhone.
If you do, when Android is the way to go. Microsoft services can actually replace Google's services (instead of just running alongside them as it happens on iOS) and everything is much more tightly integrated. There's a reason why Microsoft did that "Galaxy S8 Microsoft Edition"
4 - How picky are you about software updates (knowing neither Android nor iOS need updates as desperately as WP needs)?
If you want your phone to be updated until it can no longer run because the updates bogged down your phone, then iOS is the way to go. Apple will literally update your phone for many years (to the point of your phone not being able to actually handle the updates anymore and crawl down to a stop).
If you don't much care for updates, then go Android. There, depending on which OEM you pick, you can get updates slower or faster. If you want fast updates on Android, you have to go with either a Nokia or an iPixel. But most OEMs support their phones - well, the flagships at least - for 2 years. Some support them for longer (Sony is a good example).
Once you've answered these questions (and hopefully made the right choice
) THEN you can start the even harder task of picking a phone from the vast array of offerings no the market today
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