Which tool is better to "Design mock-ups"?

Question

As a beginner, I want to know which ones are suitable for Java, C# and Swift development. I have found many options but I am still unsure which one is more powerful, and above all, I am looking for a free one. Maybe, it would be necessary to purchase one later! If so, which one is highly recommended?!

Answer 1

Other tools that I found but it'll be necessary to check each one!

Cool Mockups, PSD Covers, Pixeden, MockUPhone, Mokk.me and NinjaMock.

Any insight of them?

Answer 2

These ones seem to be free!

(1) Mockplus, (2) Fluid UI, (3) InVision, and (4) Sketch.

Maybe, has anyone used one of them?!

Answer 3

c#