Hi Solarguys,
That is a bit of a loaded question, however I will do my best to answer. I want to start off by discussing two versions of Method, we will call them v1 and v2, v1 being the Method you are currently logging into and using, v2 being a newer version Method is working on that will be available in the coming months (I don't have an ETA at this time).
I am only bringing up v1 and v2 versions of Method because I want to make sure you are aware of a newer version being released down the road, this may make a difference in your decision on which tablet would be best for you.
Our current platform, v1, was designed to consider Desktop users first and mobile users next. v1 does have 'Mobile Optimized' screens that work best on mobile devices, tablet/smartphone doesn't really matter, however the mobile optimized screens do not work well on regular desktop environments. You may also find limited functionality when using the Mobile Optimized screens.
v2 on the other-hand considered Mobile Users first, meaning it is being designed to function best on mobile devices, then desktops. v2 will be quite a different experience then the v1 'mobile optimized' screens mostly because these screens are already mobile optimized, so you won't loose any functionality as you might in v1.
First I will discuss the difference between Android and Apple tablets. Other than the Operating System, there shouldn't be much of a difference between tablets with either of these OS's. They should likely function the same using v1 optimized screens, and they will both look incredible on the upcoming Method v2. The main consideration when designing v2 was for screen size/resolution, nothing to do with the OS being used, this is why the experience should be basically the same from Android and Apple tablets.
Now, Windows tablets can be a bit of a different story, but keep in mind there are two different types of Windows Tablets (as you originally mentioned), one is a full-blown Windows 8 environment, the other is Mobile Windows 8. The Mobile Windows 8 tablets will be similar to Android/Apple tablets, again more in regards to screen resolutions/sizes. However the Windows 8 tablet with a full-blown version of Windows 8 is a bit unique compared to the others. This version would be using an internet browser (as far as I know), similar to your Desktop browsers. With that said, it will work well for your employees on the road that are using v1, non-mobile optimized screens, and it will work just as well as Android/Apple tablets on v2.
To wrap this up, I realize there is quite a bit of information here, I just wanted to answer this as best I could. I am not sure what you have customized in Method and what screens your employees would be using on the road, this would be a key factor in decided which route to take. I would suggest figuring this out, if you are using the Field Services app in Method, then you would likely be viewing this from v1 mobile optimized screens. You should also take into consideration v1 and v2, v2 will as mentioned above should work great on all devices, however we don't have any release dates at this time.
-Ben