Iphone 6s or sony xperia z5?

I'm planning to buy a phone next week. Those two phones mentioned above are the only options i have. I need a phone that i can download lots of applications and HD games and can still perform without any Lag. Which one should i go with? And please don't suggest a new because those are the only ones available for me.

Those are both pretty new, no biggie. I'm gonna say right now that they're both going to give you a smooth, lag free, experience. However, the iPhone is the more expensive one, and the Xperia Z5 has the best camera in the smartphone industry. It's also waterproof, and has a MicroSD slot for expanding the storage, useful if you want lots of HD games. While they're both great phones, I'd go with the Z5, simply because it's more for your money. Believe me, I wish I could get a Z5, but I live in the US and now that finally Sony's bringing it here, they're stripping it of its fingerprint scanner. If you live anywhere else, or are importing it, go right ahead.