Picking best keywords is meant for pay-per-click advertisers.
Keywords analysis (of any kind including research, density, suggestion, variation, volume or geo-targeting report etc.) is useful mainly for PPC programs and campaigns, not for search engine optimization.
Just to illustrate: Google's very own Keyword tool is direct part of AdWords (which is advertising platform), NOT part of Webmaster tools. Think why.
You can easily find keywords, their variations and search volume using this or any other tool, but remember that keyword worths nothing without (quality) content behind, and quality content is far from keyword stuffed one! Keywords and phrases that trigger more search produce more traffic, and should be used to target/trigger paid ads.
For web sites, you should focus on content & visitors. Keywords will follow: all you have to use is web log analyzer (such as Webalizer / Awstats or Google Analytics) and it'll report key phrases and keywords people use to find your web site. With such reports you will soon realize that biggest part of traffic often comes from keywords and phrases that are not in the top at all (by search volume) and that is something that no keyword analysis tool can ever substitute or tell in advance. So, instead of expecting machines to do your job, rely on common sense, and: Log / analyze, see what works best for you in practice, and never search for keyword variations just to use them as primary content, which is both unethical + pointless, cause engine's algorithm is sophisticated enough to determine fake keyword density and abuse. (and was, for the last decade!)