Meh, I'm running stock TouchWiz 6.0.1 on a nearly year old note 5 and it hasn't slowed down and runs like a beast.
Too much BS in this thread. If you are using a flagship device from recent years and it's glitching and lagging, you've either got a dud device or you've screwed something up. If it's an app doing it, surely you have the nous to figure out where you've gone wrong and rectify the issue.
If it's a nasty cheap as POS, that'll be the issue, don't go spending 100 dollars and expect 500 dollar performance, if it performs, sweet, but don't expect it to be hassle free.