Hi chris-tee! Glad you like these forums.
Whether you have a TESL certificate or TESOL certificate, they are basically all the same thing. That is, they all consist of a few weeks to a few months study, require no real prerequisites to gain entry to the courses, and none of them offer advanced standing to University programs.
With a TESL or TESOL course, best to choose a provider that is recognised and has lots of publicity out there. The i-to-i course is great as many schools and recruiters know this provider. They also offer classroom based classes in locations throughout Australia if you prefer this over online learning.
Seeklearning is merely a front for Global TESOL. Probably just an agent for Global TESOL.