Is fine or medium more professional? Quick question for the more experienced folks here!

Just graduated in May as a PC provider (yay loans...!). I have forms I fill out for referrals with a template on the computer and then sign them myself. Want to step my game up a little.

Is a fine nib or medium more “professional?” Remember, this is signature only. Plan on buying a Pilot Metropolitan fountain as people love them, not ready to buy a $100+ pen, and I’m not a business man where this is in front of clients per se. Any thoughts would be great thanks!