Yes they do see a difference. Determining which is better for SEO depends on what the topic of the website is. So if it is a website about 50-cent the number might be better. If it is a topic where people are more likely to write out the word--then maybe spelling it out might be better.
Purely in terms of 50 vs. fifty by themselves, 50 wins: 68 million to 3 million.
Check out the Google Keyword tool: https://adwords.google.com/o/KeywordTool