My wife currently uses an iPhone 4, the contract is up for renewal and she's upgrading Friday. I'm trying to convince her to switch to Lumia. I own a 520 with 8.1 which is great but she's able to go higher spec - which would be the best of the Lumia range to recommend?
You don't mention which carrier you have... each of them have some exclusives.
Rather than just recommending a particular Lumia, I'd recommend going to the windowsphone.com website and comparing. A lot depends on how she uses her phone and what is important to her. i.e., if she wants to be able to shoot better quality video, the Icon (Verizon) is all about that. If better still pics and zoom are her thing, then the 1020 (ATT) would be her phone.
Additionally, you've got to look at her must-have apps. Some do not have WP versions or comparable counterparts. Other things aren't fully supported (i.e., if she connects her iP to the car, check the automaker's website for compatibility). Fitness wearables -- also a lack of support for WP, (although Wellograph offers a beautiful fully-compatible wearable, it's spendy) and MisFits is saying they have a WP app planned. Thus far, not much from FitBit.
We'd love to see your wife come over to the tile side, but it won't be a good experience for her if there are tools she uses now that she won't be able to use a week from now...
One last note: She might want to hang on to her iP for 3-4 months. There are new phones in the pipeline that have not yet made their appearance in the carrier inventory lists. And we are awaiting updates to Windows 8.1 (pending carrier approval/release).