Which is a more reliable snapshot of marketable keywords? For instance, Wordtracker shows a high number of searches for terms that show low volume on Google
Google results are based on actual searches in Google. Wordtrackers are based on a relatively small (but not insignificant) sample of search results. I tend to trust the Google results more but I'm sure others may disagree Kev
Wordtracker uses results from small metacrawlers (another form of search engine) and then assumes people who use Google etc search for the same results, and then multiply up according to the appropriate Search Engines share. Google's tools actually use Google results....Google's traffic estimator is pretty poor though, just keep to Adwords.
Wortracker uses results from meta crawler, altavista while google uses its on database. You need to use both of the results to define your keywords. if you are targeting google only then go with google keyword tool.
I think one of the key things here is getting familiar with the tools and just using it as a gauge. Don't take those numbers to heart, as the most value is in the relativeness and comparing the keywords with each other. Matt