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.