Twilio runs on Amazon EC2. Tropo runs in the Voxeo network, which has been around for 10 years and has many customers including much of the Fortune 500. Tropo can handle a much greater call and SMS volume, so if you need volume or expect peaks of usage, Tropo will be better.
Skimmed the article and came across this. This isn't very informative and seems biased.
Skimmed the article and came across this. This isn't very informative and seems biased.