A little bit of background... I love trying out different things. I'm always in search of the perfect OS. All OSs have their strengths and weaknesses and I love learning about them to use them together in different ways.
So.... I find myself in posession of an iPad running iOS7, a 2013 Google Nexus 7, and a Nokia 2520 Windows 8.1 tablet. After spending some time with each I think I've got a pretty good handle on the strengths and weaknesses of each. These are all just my opinion so take it as you will.
iPad - So this is the gold standard against which all others are judged. Not much to say about it. The GUI hasn't changed much since the iPad launched and this I think is one of its greatest weaknesses. I think the greatest strength is the AppStore... it really does seem that there is an app for everything. However, this is a tablet designed for ONE USER. There is no consolidated sign on. I recently changed the email address I was using for my Apple ID and I had to make changes on EVERY BUILT IN APPLE APP. I had to change it in the App Store, FaceTime, Messaging, etc. I should be able to change it in just one place. The Mail app allows you to have multiple mailboxes but they are all under the same app. That's fine if you don't mind other people seeing your e-mail.
Nexus 7 - Again the Google Play store is the device's greatest strength BUT there is a bunch of junk in there too. While on the surface the GUI looks very similar to iOS the ability to add Widgets to the screen is a big win. Rather than opening up a weather app on an iPad to get the 5 day forcast I can have it on my main screen so I can see it at a glance. Being a Google created OS it has the best apps for taking advantage of all of Google's content. I still don't really see it being all that great in a multi-user environment but iOS8 should take some cues from Android and add widgets. My only real problem with my Nexus 7 is the incredibly short battery life but I'm not so sure if that is a problem with the OS or with the hardware. As far as multiple users go it depends on the manufacturer. I've been told that Android 4.2 began to offer the option to have multiple users. However, some manufacturers disable it. Since the Nexus 7 is running pure Android you have that capability which is nice.
Windows 8.1 RT - You know... I really like this tablet. The app store was at first a disappointment but then I realized that I don't really need anything. First of all, this tablet comes with the tablet version of Office. SO... I've got Word, Excel, Powerpoint, etc. Not some knock off that isn't quite up to snuff. It is MADE for multiple users. In fact, if you are using a Microsoft Account to sign in on it there is nothing really to set up. If you are using your Microsoft Account to login to your desktop then all your mail settings, contacts, and calendars will automatically be synced to the tablet. Last night I was looking for a YouTube app. Silly me, there is no need for one when I can just go to YouTube in Internet Explorer. Apple needed a YouTube app initially because the iPad didn't support Flash. If you want a tablet to play games on then you will want to go with an iOS or Android tablet. But if you want a tablet to actually do work on then I'd reccommend a Windows tablet. It is perfectly possible to use the Office software with just the onscreen keyboards but I'd suggest using an external keyboard. That said I'd do the same if I were using Pages on iOS to write a document.
In summary I really think Microsoft has decided to cede the home/entertainment user to Google and Apple and is strengthening it's foothold with the business user. The Surface and the Nokia 2520 both have USB ports on the device so working on a file and transferring it to a thumb drive keeps things simple. I'd have to use DropBox or Apple's cloud drive as a go-between to do the same thing on the Nexus and iPad or e-mail a file if it is small enough. Apple needs to modernize the GUI to make it more functional. I don't like having to launch mutliple apps to get information I could get in a widget or live-tile on a Google or Windows tablet. I really can't say too much about Google. Their OS is all over the place with different manufacturers putting their own spin on it. You might like what one manufacturer has done and hate what another presents.