both of them have pros and cons:
1) ielts and toefl consist of the same 4 parts
2) to enter the ielts exam, you need to reserve a place for the day you will enter at least 1 month before, for toelf it is possible to find a place after 1 or 2 weeks.
3) try to get used to the english accent on ielts and the american accent on the toefl
4) ielts are done in classic exam mode, with pencil and paper; toelf is usually done by ibt, ie computer, of course, if you wish, you can also take the classic exam, but it is not preferred anymore.
5) there are no teachers to work with ielts, usually there are a lot of teachers to practice toelf, and there are many people who take up the judgment
6) the listening area must be filled in the ielts, it is played on a tape; there are multiple choice questions in toelf, you listen to the talk first, then the questions come, as the questions come, the section with the problem is played again. i definitely prefer to fill the gap, and time is given after you listen first. you look at your answers in ielts, then it is played back. it gives 10 minutes more time to switch to the upper answer key, you can get super points as long as you do not make a spelling mistake.
7) ielts in reading parts directly ask the question, there are tricky questions in between, but they do not break the base; toelf asks you to derive an opinion from the subject being read, and often the time given may not be enough to think about it.
8) there are two main sections in the ielts writing part, in academic ielts, a graphic or a table is given in the first part, in the second part you are asked to write essays; there are two main parts in the toelf writing part again, you are asked to read a paragraph first and then a talk about the subject, you are asked to compare or evaluate these two, and in the second part you are asked to write essays. you use your fingers on the pen toefl in the ielts.
9) while ielts speaking is done one to one, toelf speaking is done on a computer. the ielts speaking exam is done separately from the other parts, you face a live person asks you questions, you answer them, you are more humane, there is an atmosphere of conversation, whereas in the toelf, the computer guides you and the questions can sometimes be more complex because it gives a paragraph and then a dialogue is asked to evaluate these two. gives a chapter from a lesson and asks you to discuss the topic.
10) but the biggest difference i think is that during the ielts exam, someone is not talking while you are writing; as a matter of fact, you try to speak and listen in the same room with many people during the toefl exam, so if someone is still speaking while you have passed the full writing, there is a possibility that your brain will be turned over. or, while you are still in the reading section, you cannot concentrate on the paragraph and the voice of someone listening until the end.
11) one more important difference: ielts exam results are valid for 2 years, toelf exam results are valid for only 6 months.
edit: toefl exam results are also valid for 2 years.