Our school (K-12, east coast, I'm IT director) has purchased hundreds of both devices in the past 4 years. We started with 3:1 iPads in the first year, distributed evenly throughout the school. We very quickly realized that the iPad is not the right device for any student who ever needs to type anything, and the "enterprise" management from the MDM providers (who are handcuffed by the atrocious tools, including Apple Configurator, that Apple provides) is pretty awful compared to the outstanding and couldn't-be-easier management through the Chrome Management Console.

So now we purchase iPads for prekindergarten through second grade, and Chromebooks for 3 and 4. Starting in grade 5, we have a mandatory BYOD and the Chromebook is our recommended device. In the middle school (5-8) the Chromebook takes 65% of the market share (versus Apple 30% and other <5%). In the upper school (9-12) it's more a 50/50 split Apple/Google.

It's just so hard to discount the functionality of a real keyboard in any school where typing (and consequently writing) matters. Google Docs on an iPad is still awful, despite lots of improvements in the past few years. Still, if it were up to me, the lack of management tools for the Apple side (each device requires a LOT of manipulation by hand to install apps, update software, manage accounts, etc) would be the deciding factor and I'd never buy another iPad again.

Edit: I just wanted to clarify that our "BYOD" program 5-12 is a laptop program. That's 65% Chromebooks and ~30% Mac laptops in grades 5-8, not iPads. We don't allow the iPad for the program requirements, though we permit their use as long as the student also has a full-sized laptop.