Amazon has a much larger overall turnover. I believe Amazon in 2013 had a turnover of $74+ Billion in comparison to that of overstock.com which had a turn over of around $1.3 Billion.
Sorce
http://www.digitalbookworld.com/2014/amazon-booms-in-2013-with-74-45-billion-in-revenue/
Either way though overstock has a much greater interest for the overall progress and health of bitcoin as they:
- Keep 10% of bitcoin sales as bitcoin to preserve it from being dumped.
- Donate 4% to the future development of bitcoin technology and platforms.
- $1.3 M already sold through bitcoin sales.
Source:
http://www.coinssource.com/overstock-ceos-passion-for-bitcoin/
Cheers