As far as I have heard the 1520 was discontinued or not available anymore as they will be replaced by something new.
My experience was good but not great with Windows Phone. The updates were always late or I never received some of them on my 920. The keyboard was absolute garbage and if you have fat finger you are buggered. I realize that a 1520 is much larger but I was not impressed with Nokia as a whole. Battery life was bad and the 1520 especially felt like a lopsided smooth brick that would be prone to being dropped.
I did a lot of research and tried a few phones before I upgraded to my Note 4. In the end it won out because it was the best currently available specs wise. And the S-Pen just adds a few nifty extra features that makes the phone more than just a Whatsapp tool. It has the QHD display as well so it was a winner for me. I have had no real issue with it except the normal Vodacom network problems in my area. The new Touchwiz GUI is also pretty good as a standard GUI.
The LG G3 is very nice but it is prone to overheating, if your brightness is just slightly too high and you use the phone for a long time it will overheat and shut down. The QHD display also drains the battery very quickly (something the Note 4 does not do).
The HTC One M8 is a magnificent phone, build quality and its Sense GUI is something you will notice the first time you use it. It is however smooth aluminum and slips out of the hand without the tightest grips. Its sound is also suppose to be great but there is a nasty vibration to it when going full blast. The Note 4 has slight distortion if you max out the sound with youtube etc. but it is VERY loud then.
Watch out for Nokia and Windows phone, ease of use is probably their biggest selling point but the phones feel awkward and large to handle and the performance is really bad most of the time.
Best thing to do is go to a shop, like Cellucity and look at all of the phones and hold some demos in your hands to get a feel.
Another thing I forgot to mention - batteries can't be changed with the new Nokias and HTCs. Samsung and LG and others can have a replacement battery installed by yourself should your phone start suffering later on. The Note 4 also has fast charging, I charged my phone in 50 mins from 11% to 100% yesterday, sometimes it is quicker other times a few minutes longer but the max I have seen is 80 Mins and it was fully charged.
