bench_it.rb

require 'benchmark'
require 'active_support/all'
require 'httparty'

HOST = "http://listify-it.herokuapp.com"

def benchy(name, count=5)
  result = Benchmark.realtime { count.times { HTTParty.get("#{HOST}/debug/#{name}") } } / count.to_f
  "#{(result * 1000).round} ms average"
end

def bench_it(name, count=5)
  benchy(name, count) # Warmup
  3.times.map { benchy(name, count) }.inspect
end

results.rb

########################################
# RESULTS
# bench_it(to_json) - ["33 ms average", "24 ms average", "36 ms average"]
# bench_it(rabl1) - ["36 ms average", "23 ms average", "43 ms average"]
# bench_it(rabl2) - ["41 ms average", "45 ms average", "42 ms average"]
########################################

get :to_json do
 @lists = List.recent.includes(:users).limit(15)
 @lists.to_json
end

get :rabl1 do
  @lists = List.recent.includes(:users).limit(15)
  render "lists/small"
end

get :rabl2 do
  @lists = List.recent.includes(:users).limit(15)
  render "lists/medium"
end

For 'medium' we purposely used extends and partial and added a lot more attributes to measure the performance impact