Good question Greendream. For the most part I've found it really depends on the niche you are working on. Some niche's have a lot fewer searches than others so you might try and capture the 50 or so hits a small niches gets. If you can dominate the top 10 of Google then your chances of getting the lions share of those 50 hits would be good especially if most of those clicks were buyers.
I would however, try for the larger niches were you get from 50,000 to 100,000 searches. If you can find those kind of number with low competition then let me know
