Well... for tutorials/guides... the best thing is donating along with adsense if you ask me... then again if you have forums and such you may use adsense .
I fail to understand why it is so common that people say forums are worthless, I have found forums very effective. I think the difference is that most people use some third party forum script that is impossible to customize, or the user isn't a coder. My forums I have built myself and have not added AdSense to, but built AdSense within them, displaying ads between posts and such, and they perform quite well. I can't say the CTR is awesome, but the forum is high traffic and overall, brings in good money. Secondly, yes, article/information type of sites, if they have good traffic, can be great as well...
Blog is the best for earning. cuz search engine likes blog content. they will index your blog articles real soon as you post.
If your content have no better solutions then you will get higher CTR that is correct for the adsense. However, your traffics will hurt of poor quality content. You will lost the ranking and visitors therefore you will still lost the possible clicks. better if the content is good and let the visitors click naturally.