What is the best iPhone?

I need a new phone and my friend has the iPhone 7 plus, which is really good and doesn't slow down or anything. My mom has the iPhone 8 and it takes so long to load, its laggy. So i don't know what phone to get.

All phones get laggy eventually. It's impossible to get a phone that won't slow down. It also depends on usage. The most up to date Iphone is the XS Max and it's the most powerful.

I think you DO know, but you don't realize it.

Phones and computers do NOT "slow down" or "get laggy eventually" if they are properly used and looked after, that is a myth. If there's a slow down there's a cause and that can be fixed.

The iphone 8 should be faster than the 7.

You mother is probably not "killing" apps when she has finished with them, so the RAM is full of idle programs. A lot of people still do not realise you need to do that.

Just double-click the home button and flick everything off the screen, then restart the phone.

With an iphone you need to do that regularly - or just get in the habit of killing every app every time, as soon as you are finished with it, or all the open ones before you put the phone in your pocket after using it.

Smartphones are just small computers and they can get messed up in the same way as PCs.
If something gets really messed up you have to reload the operating system - but at least with an iphone you can do a backup to itunes first and restore that after the DFU reset, so you do not have to start from nothing after a reinstall, you keep all your data.

I'm still using an iphone 6 128GB I've had since that model first came out & it still works perfectly.
I'd go for the iphone 8 if I were to get a new one - always the version with the biggest storage capacity.