So out of those in the club who could play left back, I'd say I'd go with this heirarchy.
1. Santon - Obviously our best LB. Not the best fullback in the world defensively (like everyone else though) but the best attacking fullback we have.
2. Raylor - While Santon's the best attacking fullback we have in terms of movement, he's the best in terms of delivery. Injured sadly but undoubtedly an asset to the team. Over the wall.
3. Perch - He seems to do well at any position we play him these days and he could make a depleted side look decent in a jiffy.
4. Fergie - Started out as a LB so he's an obvious pick here. A bit injury-prone atm though, but he's got bags of potential and has a good attacking instinct.
5. Anita - Not sure if Tav is better than him at LB, but Anita seems to have the attributes for the role. Pace, good defensively, good vision for deliveries, stamina and composure on the ball (Something which only he and Santon possess among our fullbacks imo.)
6. Tav - Appears to me as a Simpson-type player at the moment, which could obviously change as he matures. Not a natural LB, but young and still adaptable.
7. Jonas - One of the best defensive wingers imo. Full back is clearly not natural to him but he will put in a good shift when needed.
8. Good - Not a natural fullback and not seen him much but I'll place him here as I've read he's a ball-playing leftie who seems mature for his age.