What is the difference between FTP Brute force with hydra and and FTP brute force with Metasploit ?
Both perform the same basic functionality for FTP password cracking in terms of word lists and brute force attempts. Metasploit has the added advantage that you can perform additional functions after you have gained access to the FTP service however.
I am not sure what the performance difference there will be between the two in terms of pure speed. That could make for a interesting comparison and would be the only area where a specialized tool such as Hydra could gain an advantage I suspect.