I have developed a duty roster for Esperanza Devereaux, my Swashbuckler. My choices of companions is only a reflection of how I feel about them, your opinions will very likely differ:
Top 3 for first mate position ( based on group buffs ) 1. El Toro, 2. Itzen Kaan, 3. Fan Flanders
Top 3 1. Sarah Steele, 2. Samocles, 3. Shiruku Nekko
Top 3 1. Ratbeard, 2. Subodai, 3. Birgus Latro
Top 3 1. Catbeard, 2. Gracie Conrad, 3. Lt. Springer
Top 3 1. Bonnie Anne. 2. Nausica, 3. Zeena
Top 2 1. Old Scratch, 2. Crab Hermit
Alternates I like and would use if necessary: Froggo Villa, Tricky Vinnie, Hawkules, Monkey King, & Mustang Sally. The others will be put on task. This should be enough to give interesting and challenging play. So with El Toro in the first mate position and being an SB, I would pair him with a and a for example and so on down the line.