Really confusing question... eveyone wants the best. So the best keyword tool in the whole world is your brain.
You just need to keep few things in mind.
1] What is your Product/content.
2] who is your target audience. [male/female, children/adults, geography (to know bout thr taste, buying habits and best time to target them)
3] go for trends, see whats coming in future, a new movie, festival, holidays... so you can target accordingly.
BlUeFiRe