MELAB & CAEL vs TOEFL & IELTS

[Astronomer1]

I'm a bit torn between choosing among these English exams:

MELAB, CAEL, TOEFL, and IELTS.

The motivation behind my question is to find out which one is, loosely speaking, comparatively easier or more standard than the others? Well First, I've heard there is some scaling applied to TOEFL and IELTS exams based on your range of exam-takers due to an usually fixed mean of scores. They allegedly curve the scores, so that it seems consistent with exams taken at different times of year, and the period when the applications are completed and sent (months before their deadlines), taking the exam among other applicants may be a minus. I personally do not know how much of these are actually true (to me it seems extremely unlikely that it has not been considered by the statisticians working at those test organizations).

Second, I am not familiar with first two, and I think if I can get a better result. It's not always a matter of preference, as I can tell that IELTS is easier to get a good score at I think than TOEFL. So what's your two cents worth?