They're quite different screens, LG Nanocell TVs are IPS displays. Samsung QLEDs are VA. Typically the colours have less contrast on IPS and can appear a little flat as a result, but they have good viewing angles so if you have a lot of people in a room sitting off to the sides they can be more suitable.
I think generally the Samsung's are better reviewed. Generally Samsung and Sony seem to be class leading for non OLED TVs at the moment.
What's the exact Samsung model? Generally speaking, you have to pay a fair amount to get one that is worth the additional premium Samsung charge. The lower end Samsung QLEDs are not very special. If it's a low end one you're better saving the money and getting a cheaper brand because they won't have the tech (dimming zones, brightness) to be worth it, they're pretty much the same as every other budget TV.