Blowfish and DES are both symmetric-key 64-bit block encryption algorithms. That's pretty much the end of their similarities. Blowfish is faster and more secure than DES. (Then again, pretty much anything is faster and more secure than DES...) DES is more generally available, because it's been around longer and because nobody official cares if you implement DES.
These days, I'd choose AES first, and then Blowfish, if I were looking for a symmetric cipher to use.
In Theory, there is no difference between theory and practice.<br />In Practice, there is no relationship between theory and practice.