Paste: sorted

import sys

counts = sorted(
    (
        ((sum(1 for c in line.lower() if c in {'a', 'e', 'i', 'o', 'u'}), lineno))
        for lineno, line
        in enumerate(open(sys.argv[0], 'r'))
    ),
    key=lambda x: x[0])
print(f"Line {counts[-1][1]}")