Google Keyword Search tool. Find out what people are looking for. The lower the competition the better. Good luck!
It all depends on your niche. If you are talking about competition on the google adword tool then that is the advertisers competition for the keyword so a high competition can be a good thing.
If you are trying to find out what keywords your site is best optimized for, you can do that with Tutor SEO spider. Create a project add your site to a list for crawling and you'll get result table with the best 50 keywords. Also you can input your 50 keywords to see how well is site optimized for them. Hope that was helpful!
I will suggest You google adword! I find many good and exact researches from this tool! and it will give you the best and correct results
There are planty of free keyword tools.Traffic travis, or Market samurai are free keyword tools, but google keyword tool works just fine. Also check google trends, to figure out which country to target.