In some blogs, I use "all in one adsense and ypn", but lately I have created new blogs with coded inserted directly in template, because I decided to make some changes in order to get to show Adsense in "excerpted pages". You should learn a little about HTML and do it by yourself too!
I advice you to go with MightyAdsense plugin which is best for me. All in One Adsense and Ypn is also good plugin if you wants to put your ads on different places!
Easyadsense is a good one. You have to spend a couple of minutes to configure the settings and thereafter it automatically ads the code in sidebars, header, beginning/mid/end (your choice) of posts. Pretty simple and straightforward.
I use Easy Adsense, its pretty good, you need to copy and paste the code into the boxes and it also has a search widget thingy as well.....seems to be working for me.
It's better to edit the theme and put your code in but there are many plugins available, look into wordpress plugins directory.