Hi
In general the academic module is harder. The speaking and listening papers are the same for both general and academic. Given the choice I'd take the general paper for the grade, but studying for academic
IELTS is going to teach you more.
The academic reading paper is much more challenging than the general paper and needs specific academic reading skills. Some of the texts are really quite complex and deal with specific/specialised topics. More than that the questions are tricky: give the academic reading paper to a native speaker and they would struggle - I don't believe I would get 100% necessarily and I've been teaching
IELTS for over 10 years!
In the writing the big difference is in part 1: in the general paper you get to write a letter - who can't do that? In the academic paper, you get to describe a graph. It's not too bad once you've learnt how, but it's not a very natural exercise. Part 2 is an essay in both papers and that shouldn't worry you too much.
As for TOEFL: it's similar enough and it shouldn't take you too long to master
IELTS provided your language skills are OK.