What phone should I buy?

Actually my dad needs a new phone. He was first introduced to smartphones with a cheap android and hated it (no surprise). He moved to windows phone and liked it and then has been using a Nexus 4 for the past year. He washed his Nexus 4 and it is not working and has now decided that it is time to get a new phone.

He wants a Windows Phone. His Nexus 4 was a ride for him, and he was almost constantly complaining. From accidental call to cant figure out how to do things, he was sick of it. Also judging by how his notification tray was always full, he didn't know how to use it.

The dilemma is that there is not a fairly new windows phone to buy. The only one that seems worth buying right now is the Icon, which is a Verizon only, and we are on T-Mobile. The 1520 is large and expensive without much use imo (unless someone gives me a really good argument for it). The best phones I see right now are the 1020 and 925 which both seem near the end of their cycle and are likely to be updated. Also with WP 8.1 around the corner (almost makes me want to switch to WP) I want to make sure he gets a phone that will be updated to that.

Another option is to get a 520 right now and upgrade later on in fall (when hopefully something nice comes out), and hand the 520 off to my younger brother or relatives in India. Do you think the 520 will be updated to 8.1?

The last option could be to revert back to an aging 710 and then get a new phone in April as soon as one is announced.

tl;dr: What should my dad do if he wants to go to Windows Phone right now?