I have a Nokia Lumina...i dunno 770... LOL I'm probably one of the few people here who has a windows phone, and I've owned iPhones and Galaxy's in the past.
My opinion is meh, Android is best.
Windows phones have some perks, but there are also some big flaws, and since apps is the first thing you mentioned, then the windows phone is probably not for you. Not only are there less apps on windows phones, the infrastructure of windows phones is stupid. e.g. I had to download my weather network app from the website on the browser, it wasn't available in the marketplace when I downloaded it (still might not be).
Also with a windows phone, you are forced to use the "bing" search engine, which is a real peice of crap. There is a google search app, but it's not a browser, so it's really annoying when you want to search something. Unless you open a separate app, you're forced to use bing search. Google maps are still available, but I have GPS off on my phone to save power, and every time I load google maps it says "GPS is off, blah blah, blah."
iPhone is a bit better then a windows phone, but I still don't like is. A lot of aps, like Angry Birds, are free on Android devices, but cost money on Windows Phone and iPhones. Plus with Android Phones, you're allowed to get apps outside the app store, and there are so many apps for it. e.g. I have a GBA emulator, and my friend has an N64 emulator. Can't do that on iPhones.
Another app I had on my android phone was one that allowed you to download songs directly onto your phone. I was real lice because you should identify a song with shazam/sound house, and the download it minutes later onto a custom playlist. I listened to a lot more music on my Android because of this, and I would even say that my taste and knowledge in music grew too.
So in terms of convienience, I say Android Phone. Even if none of the problems I listed apply to you, there are a lot of annoying loopholes you have to jump through to get apps which are easy to get on Android Phones. I can't comment on camera/performance, etc, because my phone is out-dated.
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P.S. I bought my windows phone, not because it's a windows phone, but because it's a Nokia, and I wanted a reliable phone. So far, it's much much more reliable then the iphone. I've owned my phone for over a year, and it's only frozen once. I'm not gentle with my phones at all, within 1 year, my iPhone started to have serious software glitches, and my lock screen button broke, so I would have to wait a minute before the phone locked. By 1.5 years the other button stopped working, and it was a monthly trip to the repair shop. I eventually just gave up when buttons just started to fall off. I still have my iPhone 3GS, but it can't charge, the buttons don't work, the volume button doesn't exist anymore, and the battery is dead. LOL.
Can't compare to my Galaxy because after only a year I dropped it in the toilet, and flushed....... Until then it had 0 issues though, so I can confirm it was doing a lot better then my iPhone.