Had the s3 which started lagging a lot (think it was after an Android update) and even though it was half way through my contract, I just went and bought an iPhone 5s. A year and a half on, it's working as smoothly as it did when I bought it. No android lag. Doubt I go back to android any time soon. In fact I wish I could just have a newer version of a 5s as opposed to the larger 6! I have a 6+ for work but that's not with me at all times like my personal one.
Phones from 2013 and beyond do not lag in general use at all. Of course if you install hundreds of memory hogging apps and widgets, of course lag will be felt. Hell, even my 8 GB Ram, Core i7 laptop gets bogged down time to time!
Of course the Iphone will not lag. It is a severely limited OS that APple wants you to use in a certain way. You cannot install apps outside of the store, you cannot copy media files directly into it, you cannot have multiple apps RUNNING (and not suspended) in the backgrond, you cannot use apps like MU Torrent as background downloading is not permitted.... plus a shit load of other stuff you cannot do..
On the other hand, a good android phone is effectively a mini computer. You can do 95% of the things you can do on a PC!
The iphone 'just works' fine and provides a simple and trouble free experience to users. It does the 'thinking' for the user so its very popular with older people as well. The 'walled garden' approach works great for users who do not use their phones for more than browsing and casual games.
Try doing some serious photo/video editing on an iphone and see how you fare
I am not even mentioning stuff like inability to have more than 3-4 tabs open AND loaded in Safari. The older tabs keep reloading again and again as you have just 1 GB of RAM. And forget about loading tabs in the background. You have to WAIT for the tab to load completely instead of just switching to another and let it load in the background.
Do not want to start the ios vs Android nonsense again so cutting it short here. Both the OS's have their own market segments with some overlap. Brand equity and loyalty combined with the 'coolness' of owning an Iphone have made Apple pretty much invincible in the market. Doesnt mean they have the best OS or hardware.