iPhone 4 or Lumia 720?

Hey guys!

First of all, I live in a developing country, where our phones cost at least double what they cost in the US or Europe.

So, I just got my first iPhone, a white iPhone 4 16gb. It's beautiful and all that... but it's sloooow. I've been using Android since 2012, I had a Galaxy Nexus and a Galaxy Note 2, and I'm really tired of it. Besides, I have a Galaxy Note 8, so all my Android needs are fulfilled by the tablet.

I reealy wanted to get an iPhone and just be happy with iOS, I used my girlfriend's 4S for a week and I was pretty happy with it, but I couldn't afford one, so I picked up the iPhone 4. Unfortunately, it was a really different experience from the one I had with the 4S. Games are difficult to play, since they run very slowly, you can't rely on its performance when using apps (for instance, my favorite app is Mailbox, and I just can't use it, since it crashes all the time). I don't watch youtube videos on it, because the app is very slow, gaming, again, is very limited, since I don't even try to download games like Angry Birds Go, or Sonic Dash, 'cause I know they'll either crash or be very laggy.

I don't want to go back to Android because I don't find it a nice experience anymore. I was an early adopter of Windows Phone, I had a Lumia 710 for a year and... well... you know how that went. I had that phone for a whole year, and that was surprising to me, since I never had a phone for so long. But when WP8 came out, things were very disappointing, I tested 7.8 and it was slow, plus I knew that the app development for WP 7.x would cease to exist, so I switched to Android.

That being said, I want your opinion. I love the 720's design, and Windows Phone, but I'm afraid I might not get the complete smartphone experience I'm looking for. What I want basically is a reliable operating system that has those basic apps that everyone uses (basically the most common social networking apps), SOME gaming, not that much, I know that windows phone is not very strong at that, and I want a smartphone that will last me at least a year and not disappoint me, something that I think the iPhone 4 will do, since it's already disappointing to me.

I'm not really tied in an ecosystem, Gmail is my default email, and GCal is my default calendar, but I could move everything to Outlook.com pretty easily.

Thanks in advance!