Which took more effort between the two, cracking UPSC Civil Services (IAS, IFS, IPS et al.) or cracking IIT?

I was selected in IIT twice (1983 &1984) and in Civil Services Examination in 1990. Let me share my own views about the difficulty level of IIT and CSE.  
1: Getting into IIT
You can get into IIT, if your fundamentals are clear and you have the ability to understand complex problems. Everyone can’t get into IIT. You require a basic level of intelligence and analytical mind to get into IIT. If you don’t have it, you can never get into IIT, even you try 10 times (only 2 attempts are actually permitted now).
2: Getting into Civil Services
Getting into Civil Services is a matter of chance as well as abilities. The most important parameters for Civil Services are your ability to memorize things and reproduce it in a beautiful manner. Hence your handwriting, your memory, your command over language plays very important role. You should also understand that CSE is very subjective and luck factor plays very important role in your selection. The syllabus of CSE is virtually infinite. Hence, you should be lucky that the questions are asked from the matter which you have prepared. Further, you should be lucky that the examiner shares the same views as you write in your answer. The same answer can give you best marks and also an average or even bad marks, depending upon the mood of the examiner, his own ideals and world-view. The interview is very subjective. You will find that the same candidate getting  excellent mark one time while scoring very poorly next time with better preparation, because the Board is not favorable to him. In IIT, there is no subjectivity at all at the examiner side, as all questions are objective. 
Hence, if you wish to succeed in CSE, be ready for long preparation. The more attempts you write, the better are the chances of your selection and getting good ranks. I have seen people getting into IAS among the top ranks, who did not even get selected in earlier attempts or got a very poor rank. Some officer gets top rank in their fifth or sixth attempt. Hence, the more time you are willing to give to CSE, the better are your chances of success. The best thing is that anyone can try for CSE and get success.