4d9 > 6d6

dice.rb

sums_4d9 = [1, 2, 3, 4].repeated_combination(9).map { |roll| roll.inject(:+) }
sums_6d6 = [1, 2, 3, 4, 5, 6].repeated_combination(6).map { |roll| roll.inject(:+) }

wins_4d9, wins_6d6, draws = 0, 0, 0

sums_4d9.each do |four|
  sums_6d6.each do |six|
    if four > six
      wins_4d9 += 1
    elsif four < six
      wins_6d6 += 1
    else
      draws += 1
    end
  end
end

total = wins_4d9 + wins_6d6 + draws

puts "Matches:      #{total}"
puts "4d9 wins:     #{wins_4d9}"
puts "4d9 wins %:   #{wins_4d9 / total.to_f}"
puts "6d6 wins:     #{wins_6d6}"
puts "6d6 wins %:   #{wins_6d6 / total.to_f}"
puts "Draws:        #{draws}"

Output

Matches:      101640
4d9 wins:     55948
4d9 wins %:   0.550452577725305
6d6 wins:     40641
6d6 wins %:   0.3998524203069658
Draws:        5051