The purpose of intelligence is a tough question to answer. Its purpose encompasses a vast majority of things. In my personal opinion it really depends on what your mission is, who you are providing intelligence products to and why the information is needed. Normally intelligence answers set questions established by commanders, and these can be changed at any point in time. Intelligence is a complicated beast and for one try and tame it is simply madness. In the intelligence community many things are left open due to the simple fact our missions, technology, capabilities and intent are changing constantly. Further, I don't feel there is a right or wrong answer to this question. Only good points that any intelligence professional should really consider when providing any type of support to anyone.
For the question of which -INT is the best. Ha, I see many professionals get locked into their own little worlds and forget that they need every bit to paint a complete picture. There is a reason to why there are different disciplines in intelligence. Each intelligence provides a key piece to the artwork. HUMINT brings the human element of what locals know about the enemy and the local populaces sentiment to coalition forces. SIGINT has a few sub disciplines, COMINT, ELINT, FISINT, and MASINT. Each of those SIGINT subcategory has to deal with some type of electronics or RF energy. IMINT is imagery intelligence information provided from pictures taken by cameras to satellites. As you break down each discipline you can start to see why each is important to the other and why each needs each other to paint the complete picture. To ignore one is to increase your chance to get someone killed on the battle space. To be an analyst is not only to be technically proficient, but to be creative and artistic. Intelligence is more or less an art. The best analyst are ones who are creative and who aren't afraid to make analytical leaps to help try to bridge gaps and understand information. Granted there are technical aspects to intelligence and people can take that slap it on a powerpoint, and yes it is true and its does provide somethings. But, they could provide so much more. This profession is an intimate one, you have to hate, love and understand your enemy. You have to know his insides and outs, where he eats, sleeps and works. If an analyst fails to realize this he is not only neglecting his duty, and he is failing the entire purpose of intelligence.
I have worked at division level for the Army in Afghanistan and at the agency. Each day I have ever gone into work I have never done the same thing. I have watched the purpose of intelligence change day to day. To put a stamp of the purpose of intelligence is to hinder its entire intent. I have seen the frustrations of operators because they feel they are being slighted on information and they start to gather this opinion that we are useless. A lot of time we are restricted due to classification issues. Most of the time these issues can be overcome by simply rewording and leaving out some information without destroying what is trying to be stated. But again this is why I say intelligence is more or less an art because you have to get creative with how you plan to disguise where the information came from in order to be able to push it down to lower levels.
I probably didn't answer any questions, but I felt like I should put in my two cents. Sorry if any of this was redundant; guess it just re-emphasizes how import somethings is. Feel free to lay waste.