Spoiler
Definitely unstack the bloated midpoint. Then it's a question of whether to keep moving and slot the 5, unstack the 6, or get the runner going.
He's got 9 checkers in the zone right now, and will have more in a roll or two, so there's no better time than right now to get the runner moving. I like the spare on the 8, and 6/3 accomplishes little, so 24/21 it is.
XGR++
Spoiler
XG likes the herd's play best, although 13/5 is not too far behind.
XGID=----B-DbB---dFa--c-e----A-:0:0:1:53:0:0:0:13:10
X:Player 1 O:Player 2
Score is X:0 O:0 13 pt.(s) match.
+13-14-15-16-17-18------19-20-21-22-23-24-+
| X O O | | O X |
| X O | | O |
| X O | | O |
| X | | O |
| 6 | | O |
| |BAR| |
| | | |
| O | | X |
| O | | X |
| O X O | | X X |
| O X O | | X X |
+12-11-10--9--8--7-------6--5--4--3--2--1-+
Pip count X: 150 O: 153 X-O: 0-0/13
Cube: 1
X to play 53
1. XG Roller++ 24/21 13/8 eq:+0.036
Player: 51.83% (G:5.94% B:0.17%)
Opponent: 48.17% (G:7.50% B:0.16%)
2. XG Roller++ 13/5 eq:+0.006 (-0.030)
Player: 50.30% (G:8.37% B:0.22%)
Opponent: 49.70% (G:8.61% B:0.21%)
3. XG Roller++ 13/10 13/8 eq:-0.003 (-0.039)
Player: 49.77% (G:8.90% B:0.24%)
Opponent: 50.23% (G:8.71% B:0.22%)
4. XG Roller++ 13/8 6/3 eq:-0.038 (-0.074)
Player: 49.28% (G:8.23% B:0.21%)
Opponent: 50.72% (G:9.52% B:0.23%)
5. 3-ply 8/3 6/3 eq:-0.077 (-0.112)
Player: 47.79% (G:9.61% B:0.27%)
Opponent: 52.21% (G:10.38% B:0.27%)
eXtreme Gammon Version: 2.10, MET: Kazaross XG2