I have a job offer that requires either of the following scores.
TOEFL iBT 94
I assume all around the 70 Percentile Mark
I did my GMAT in the past and only scored 29.
I am a native English speaker
My weakness was sentence correction.
Gmat Reading comprehension was a piece of cake and I think listening wouldn't be much of a problem.
Could you advise which would be the easiest to obtain (with least preparation)?
I have no experience of IELTS but since I took TOEFL twice the last two months, I can assure you that if you are that good at GMAT reading comprehension the TOEFL reading will be ridiculous (only thing you should worry about is that you may loose your concentration because the passages are long and boooring). Listening is easy (all listening parts are very easy to understand). Speaking is tricky. You have to practice that part. Writing ... is just writing.