The Trinity course is 160 hours, 20 of which are a Practicum module. There is no difference between online and on-site for the theoretical components. It only depends on your preferred method of study. You also have the option of taking a 20-hour Practicum after the online program.
There is, however, a difference between courses. You will see that the average price of an online 100-hour TESOL/TEFL course is $300. These courses, including Ontesol’s 100-hour course, are simpler than a Trinity program, the 250-hour course, or the online CELTA. The benefit of taking one of these standard courses is that you can learn the basics. Most schools don’t ask for advanced certificates (Requirements vary a lot on a country basis), but it’s recommended to upgrade your credentials if you will continue to teach after the first year. If you are going to take one of these courses, it’s also important to pick one that teaches how to create lesson plans.