I've spent a lot of time and effort with WindowsPhone 8.0 and 8.1. I have also spent a lot of time and effort with Androd (from 2.3 to 4.4), with iPhone up to 8.4 and with my BlackBerry 9900 OS 7. Sorry, I don't do BB10 - maybe some day. I like BIS for my company business.
I converted to Windows 8.0 and 8.1 for a full year. It's by far my favorite GUI on any phone anywhere. If it had a few more apps that I personally need (like Banking), I'd carry it as my 2nd phone. I had to drop it (lack of Banking and a few other key apps) and now carry an Adroid 4.4 as my 2nd phone. I must admit, Android has come a long way in their GUI, Apps and Widgets. It's a very robust platform. iOS is there because it works for so many. Personally, I'm not a fan of the big button, with hunting on screen for back and menu buttons. I prefer Android's back and Menu and the fact that you don't have to plaster all of your apps on screens. Sure, you can put them in folders on iOS, but that's it. Android lets you keep them hidden totally in an App menu, and put icons or widgets on screen when you see fit. Better for the GUI from my point of view. But iOS apps are a bit more beautiful and elegant on many apps. They still have the app edge IMO. Windows has a lot of catching up to do.
I am a creature of functionality and efficiency and convenience. Many of us are. iOS and Android do a lot of things conveniently for you. As does the old BIS BlackBerry Platform. No you say? BlackBerry is at the very bottom of productivity? Hmm. Well, BlackBerry Travel can run circles around TripIt or WorldMate for travel AUTOMATICALLY plugging in to your calendar with reminders for business travel. NO user interaction required, EVERY SINGLE TIME. Nobex Contacts is the best auto contact capture I have ever used on any platform. Invitations from colleagues to attend meetings or WebEx or GOTOMEETING similar online meetings are easily accepted and responded to automatically, and email... well, email is what BlackBerry was DESIGNED to do.
So we have come full circle to Windows. It's by far the most elegant GUI that I have ever used. I love the live tiles. I like most of the apps that ARE available, but there are some that are sorely lacking in functionality. Then there are inherent flaws in the OS for certain things that I have desperately tried to bring to MS attention both online and in their stores. Among the most severe of these FOR ME, is the invitation acceptance flaw for things like GOTOMEETING invitations. You get invitations, you accept them, and voila! Once you accept, rather than the OS populating your calendar with the details of the meeting, it simply sends the acceptance, AND FULLY DELETES the original invitation, and only puts "GOTOMEETING XXX Time XXX Date" in your calendar. How nice. With WHOM? About WHAT? What is the dial in number? What is the web address? Oh, wait, it's all been deleted by the WindowsPhone OS when you accepted the invitation, and you didn't write it down. Why would you write it down? Whether or not you have installed the GoToMeeting App, the acceptance is independent and is a calendar function with or without an ICS importer. It SHOULD populate all the details in your calendar, right? Wrong. So you can just call and find out the details from the meeting organizer if you remember whom that was. Sure, you are the only one calling, because you are the only one using WindowsPhone, and you look like a disorganized goofball, but that's life, right? Major flaw in the OS. Major. Windows needs to FIX THIS.
Still, through all this, I like WindowsPhone. I'm glad it's here to stay, because I believe some day, I'll bury the Berry for Business (I have to retire sometime, yes?) and ax the Android, and be left with WindowsPhone. Sorry iOS. You are just not my cup of tea. WindowsPhone, you are beautiful. Seriously. Just fix some issues and do what you can to get developers back. You can't loose banking apps like Chase and expect users to be OK with it. Some of us need to have remote check deposit. Some of us need to actually accept meeting invitations and have the data saved in our calendars. Some of us need XYZ app, just because we need it.
Hopefully, all these issues will be resolved in a year or two. I hope so.
Finally, CORTANA. Personally, I think it's the best personal assistant out there. It needs to be broken out from the phone because it's that important. I've used Siri extensively. I've used Google Now (voice) extensively. Cortana has the edge. Her location based reminders are superior. Her personality is superior. Her voice recognition is superior. Her power over the phone is superior. In some areas, she is about equal to the others, but in most cases, she is better. Her music recognition is outstanding. The integration into calendar is wonderful, and it's a better all around experience using Cortana. Then, there is her singing and joke telling. OK, that's a crazy playful thing and has nothing to do with productivity, but it does make the phone a little more "fun" as I have heard some people say. I tend to agree.