From the methods outlined in the thread so far, I think I'd pick Akamai after a quick test of each of them. (results in the following are based on the 'real' value returned in a 'time' command

  Google 'ping' "baseline" from my ISP
     20 packets transmitted, 20 packets received, 0.0% packet loss
     round-trip min/avg/max/stddev = 19.858/23.823/31.484/2.593 ms

  #/SITE/METHOD
  #1: myip.opendns.com (dig)
  #2: whatismyip.akamai.com (curl)
  #3: ifconfig.me (curl)
  #4: ip.nux.ro (curl)
  #5: icanhazip.com (curl)

  RESULTS

  #1      #2      #3      #4      #5
  0.051   0.144   3.45    0.24    0.333   
  0.05    0.143   7.229   0.237   0.106   
  0.053   0.147   1.986   0.246   0.103   
  0.047   0.143   7.065   0.246   0.109   
  0.045   0.145   2.15    0.257   0.102   
  0.046   0.141   4.301   0.273   0.113   
  0.05    0.141   2.763   0.242   0.103   
  0.048   0.144   3.685   0.251   0.114   
  0.045   0.149   15.312  0.256   0.195   
  0.047   0.148   5.091   0.244   0.118   
  0.044   0.144   2.637   0.248   0.133   
  5.038   0.142   1.535   0.247   0.109   
  0.049   0.143   7.065   0.238   0.115   
  0.044   0.146   4.098   0.241   0.106   
  0.05    0.145   1.665   0.248   0.216   
  0.05    0.142   1.365   0.261   0.108   
  0.051   0.143   2.509   0.256   0.159   
  0.046   0.17    5.323   0.245   0.109   
  0.044   0.141   83.252  0.246   0.117   
  0.05    0.145   1.435   0.242   0.119

  0.048   0.144   3.685   0.246   0.113 MEDIAN
  0.310   0.145   8.551   0.248   0.135 AVERAGE
  1.144   0.006   18.377  0.008   0.057 STDEV