Stick with the iPhone. Seriously.
When I compare my Moto X to my freaking iPod touch 5g, the iPod touch 5g is better in many many ways. It feels snappier and more immersive. I can use it longer without feeling dizzy. Android phones definitely win on specs, but because of some fundamental software architecture choices iOS devices punch way above their weight. Like, 1gb in iOS is worth at least 2gb if not more on Android devices.
If iOS, Android, and Windows Phone were released today and had not come out in that order over the course of a few years, I honestly think Apple's market share would be around what they have in the desktop space. iOS is uglier and it's UI less suited for mobile than Windows Phone, and it's less flexible or customizable than Android.
But since iOS does have the headstart over the other two, there is something to be said about having the priority ecosystem for a lot of developers.
I've been using iOS since iOS 4 (on the iPad 1), Android since 4.1/Jelly Bean (Nexus 7), and Windows Phone since 7.0 (Dell Venue Pro), and as hardware and software has matured on all the platforms iOS is still the one I can't stand to use on a phone. It seems to better on the iPads, but iOS 7 especially was one step forward and two steps back for Apple as far as UI. I don't care if it's snappy because Windows Phone and Android are - for all intents and purposes, I don't care about benchmarking - as snappy on equally priced hardware, at least from devices like the One M8 and the Lumia 1520, which I've personally owned and compared head-to-head with the 5S. If you are
that sensitive to speed that it makes you dizzy to use Android that sound more like a specific medical condition applicable to you and a small subset of users than something that would bother most people (much like how iOS 7 purportedly was making people nauseous when it was first released).
There isn't anything "immersive" about iOS on an iPhone to me: the interface alternates between eye-searing white and overly-bright pastels, while managing to have tiny touch targets and icons as a holdover from 2007 (and the translucencies are Vista-esque). "Frustrating" is the word I'd use. Parallax and the animations they use don't add much, either, and on a screen of that size I'm not sure how immersive it could really be unless you are using it as an AR/VR device like Google Cardboard.
Apple was supposed to have moved away from skeumorphism, but they did a half-assed job and iOS doesn't look consistent. Android, on the other hand, has moved toward a more consistent aesthetic and has only gotten faster, even on low-end devices.
I'm not locked to any ecosystem so if the iPhone 6 and iOS 8 are actually a big improvement I may just buy an iPhone, but it really would have to be a drastic departure. The iPhone used to be the prettiest phone in town, but I'd say HTC has them beat there, too.
Vivi, I doubt you'll regret going to Android, especially if you are a power user. Doing stuff like SSHing into a server is way better using an app on a 4.7" to 6" device than a 4" one; you have access to root if you want on Android, which allows for overclocking, using firewalls, better battery management and backup, etc.; you can actually use microSDs (Windows Phone 8.1 has native app install to microSD support, as well) and USB OTG; NFC support on most mid-range and high-end phones (on Windows Phone as well - possibly coming to iPhone 6); and you don't have to jailbreak to get apps from third-party app stores (there are some trustworthy open source sites I like to use in addition to Play). The OnePlus One looks to be an excellent phone, too, and makes much more sense at $300-$350 than an iPhone at $600 to $700.

Pocket that difference and you could easily get all the paid apps you might need with plenty of money left over. The M8 is a very good phone, though, so I might give a slight edge to that even after considering price. But the next iteration is coming out soon, so I would probably wait till fall.
I can't think of a single "must have" iOS/iPhone feature that would tempt me to switch over to an iPhone right now.
Note: all that said, I'm actually in the processing of building a Pi phone for fun

But it's much lower specs than almost all smartphones, and more expensive than the OPO when all is said and done...