replacing iPhone 4: iP 5, Samsung SIII, HTC One, or WP?

Hello all.

I've been hanging with my iPhone 4 for some time (running iOS 5.11) but recently I have been more and more annoyed by the slowness. I need a new phone with a good camera and LTE tethering. I am somewhat platform agnostic, although iOS has an edge for ease of migration.

Here's my current footprint: Lenovo X1 Carbon, Office 2010, Evernote, Dropbox. Gmail mail and calendar, etc. On the iPhone, I am a big user of Evernote, including a lot of taking picture of documents so I can throw them away. Evernote is the biggest performance problem on the current phone, so I want to ensure that it works well and that their app for the platform I move to is solid, and fast. (I have no experience with the Android or WP app) Dropbox is a key for reading, as well as Pocket.

I do a lot of tethering. One of my great annoyances is the 3-step process to 'wake up' the Personal Hotspot funcitonality on the iP4, which stops broadcasting if nothing's connected for ~10 minutes.

I do a lot of texting, Facebook and Facebook messenger, G+, Skype, playing iTunes-based music as well as FLACs (using FLAC Player) .

Speed is important to me: I am a 'power user' in the sense that I want to be able to switch apps, load subway schedules, bring up images, etc., without waiting around. To the extent possible I'd like a year or two of future-proof-ness: I want to be able to run iOS 7 on the iP5 with very good performance, or the equivalent upgrades on the other platforms.

I'm open to input... Thanks in advance.