#1
One website lists the most common words in English at the URL:

www.world-english.org/english500.htm (external - login to view)

Yet taking a sample and googling the top five words, the results are:

1. the 4.8 billion hits
2. of 4.5
3. to 5.6
4. and 4.4
5. a 7.3

The word to gets more hits than the when it is googled. It gets more mixed up the more you check. These web sites never show their methodology on how they pick the most common English words. Google seems like the best system to me to find the most common words.