Which one is better for buying ? Dell Inspiron 3543 core i7 5th generation OR Dell Inspiron 5559 core i5 6th generation?

The i7 is better. Both have 4 physical cores, but the i7 has hyper threading, which gives you 8 logical cores, meaning better performance for applications that benefit from multiple cores.

I concur with @ragingloli I have the Dell i7 and very pleased with its savage performance.

@ragingloli not correct , these are both dual-core CPUs, with Hyperthreading (so 4 logical cores).

They’re built for laptops, and low power consumption is the primary goal, not performance. You can’t compare desktop i5s and i7s with the similarly-named mobile processors.

Also, @markmagdy, you have to define “better” based on your needs. There are a lot of factors besides CPU. Size, weight, screen size, screen quality, battery life, ports, etc.

That said, looking at just CPUS, I think these are the chips:
Intel Core i7–5500U (Dell Inspiron 3543) Intel specification page
i5–6200U (Dell Inspiron 5559) Intel specification page

When comparing CPUs, here are my steps:

1)
Check performance score at Passmarks CPU Benchmark page
i7–5500U score 4300
i5–6200U score 3938

2)
Check power consumption
i7–5500U 15 watts
i5–6200U 15 watts

These processors are very similar so far

3)
Graphics. I don’t pay attention to this because for my needs, they all perform the same. I am not gaming or doing VR development.

But this might make the decision for you if the laptop uses the CPU graphics, not a discrete Nvidia or AMD card.

The i5 chips offers Intel HD Graphics 520
The i7 has Intel HD Graphics 5500.

I don’t have an opinion of the graphics. If that is a factor for you, you should look up the specs.

@Call_Me_Jay
Now that is almost fraud. Fuck Intel.