bm.rb

require 'benchmark'

def regular(a, b, c)
  [a, b, c]
end

def keyword(a: 1, b: 2, c: 3)
  [a, b, c]
end

def hash(a)
  [a[:a], a[:b], a[:c]]
end

number = 1000000
Benchmark.bm(4) do |bm|
  bm.report("regular") { number.times { regular(4, 5, 6) } }
  bm.report("keyword") { number.times { keyword(a: 4, b: 5, c: 6) } }
  bm.report("hash")    { number.times { hash(:a => 4, :b => 5, :c => 6) } }
end

gistfile1.txt

tobi@box ~/tmp » ruby bm.rb 
           user     system      total        real
regular  0.170000   0.000000   0.170000 (  0.176344)
keyword  1.680000   0.010000   1.690000 (  1.677325)
hash   0.790000   0.000000   0.790000 (  0.794840)