您可以使用pd.Series.mode并提取第一个值：

res = s.mode().iloc[0]

这不一定是低效率的。与往常一样，对您的数据进行测试以查看适合的数据。

import numpy as np, pandas as pd
from scipy.stats.mstats import mode
from collections import Counter

np.random.seed(0)

s = pd.Series(np.random.randint(0, 100, 100000))

def jez_np(s):
    _, idx, counts = np.unique(s, return_index=True, return_counts=True)
    index = idx[np.argmax(counts)]
    val = s[index]
    return val

def pir(s):
    i, r = s.factorize()
    return r[np.bincount(i).argmax()]

%timeit s.mode().iloc[0]                 # 1.82 ms
%timeit pir(s)                           # 2.21 ms
%timeit s.value_counts().index[0]        # 2.52 ms
%timeit mode(s).mode[0]                  # 5.64 ms
%timeit jez_np(s)                        # 8.26 ms
%timeit Counter(s).most_common(1)[0][0]  # 8.27 ms