Patrick McCaw has the best winning percentage in the playoffs when playing 20+ games, winning 87.5 percent of the time.

highest playoff win percentage by a player in their career with 20 games played
Interpreted as:
highest playoff win percentage by a player in their career with 20 or more games played
McCawSchaeferLueEdwardsMcAdooSpriggsBrownWaltonFerrinKingBellFernstenBurrellClarkMikanCookLooneyIrvingMilicicSmithPollardCunninghamGreenThompsonConley.875.864.810.810.808.800.787.776.759.754.750.750.739.732.729.725.714.714.714.708.708.704.699.699.697
NAMEGPW%MPGPPGRPGAPGSPGBPGTPGFGMFGAFG%3PM3PA3P%FTMFTAFT%MINPTSREBASTSTLBLKTOVPF+/-
Patrick McCawPatrick McCaw32.8757.72.21.20.60.40.10.10.71.741.80.30.833.30.50.588.2245703920133419+7
Herm SchaeferHerm Schaefer22.8648.02.12.96.643.82.12.587.01754734
Tyronn LueTyronn Lue21.8108.12.30.60.80.70.00.60.92.338.80.30.837.50.20.280.01704813171411215+17
Franklin EdwardsFranklin Edwards21.8106.33.50.71.00.40.00.41.22.548.10.00.0100.01.01.284.61337314228087
James Michael McAdooJames Michael McAdoo26.8084.01.31.00.10.20.20.10.50.954.20.10.240.00.20.450.01043325255311-34
Larry SpriggsLarry Spriggs30.8009.95.02.31.30.20.21.11.83.551.90.00.10.01.31.776.52971496840563350
Randy BrownRandy Brown47.7876.01.60.60.50.30.10.40.61.538.60.10.150.00.40.573.92817429221531846-70
Bill WaltonBill Walton49.77624.410.89.13.00.71.71.24.78.952.50.00.00.01.42.167.31,197528444145328336149
Arnie FerrinArnie Ferrin29.7597.14.72.32.47.233.82.23.268.52053367113
Stacey KingStacey King61.75411.84.32.20.50.30.20.81.53.739.20.00.150.01.41.973.77192641363121155098
Jordan BellJordan Bell32.7508.72.62.10.80.30.50.31.12.054.00.00.00.00.40.858.32798266261016831+32
Eric FernstenEric Fernsten20.7502.30.70.60.10.10.20.10.20.730.80.00.00.30.462.546131111424
Scott BurrellScott Burrell23.73911.93.72.00.50.90.10.51.53.344.70.30.928.60.50.684.62738546112131133+21
Ian ClarkIan Clark41.73213.76.01.30.90.50.00.72.34.847.50.72.035.40.70.890.356324553382222955-17
George MikanGeorge Mikan70.72936.624.013.92.28.019.940.47.910.178.61,5001,680665155305
Quinn CookQuinn Cook40.7259.84.11.10.70.20.10.31.63.742.90.51.729.00.50.686.43921654228731227-42
Kevon LooneyKevon Looney42.71419.55.64.40.90.60.50.52.53.962.40.00.00.00.71.258.081823518339261921100+154
Kyrie IrvingKyrie Irving70.71436.423.43.64.81.40.62.28.618.945.52.36.039.33.94.488.32,5461,6392513379841155158+413
Darko MilicicDarko Milicic21.7147.12.61.20.30.10.20.31.02.148.90.00.00.51.050.01505525625613-12
Greg SmithGreg Smith24.70832.611.28.52.44.99.352.71.52.656.57832692055879
Jim PollardJim Pollard72.70840.113.68.13.64.814.333.93.95.275.01,724977407259205
Dick CunninghamDick Cunningham27.7045.61.71.40.20.71.550.00.30.463.61514739522
Draymond GreenDraymond Green123.69935.612.59.36.11.61.52.64.49.944.51.23.731.52.53.473.74,3761,5361,149754197180325458+888
Klay ThompsonKlay Thompson123.69937.219.34.02.21.00.51.87.216.244.23.07.341.51.92.284.14,5702,37248627211966220336+554
Gene ConleyGene Conley33.69714.65.16.70.32.15.737.40.91.461.748216922211119