What video software should I use to make my book trailer?The answer to that question is: Whatever video software you know how to use! But since you're here, and maybe looking for a more complete answer than that, I will give you my opinions on several video editing software options.
I must warn you that I am heavily biased towards using a Mac to make videos. My preference for Mac stems from my video projects repeatedly CRASHING on a PC.
I used to create videos on a PC using MovieMaker. I loved MovieMaker, except for this limitation: I could upload my MovieMaker file, but I couldn't record it onto a dvd. I found that extremely frustrating. I don't know if it's changed or not since I haven't used Moviemaker in several years. However, Moviemaker is intuitive (a fast learning curve) and that is huge for a beginning video editor (which I was at the time). However, it crashed. All the time. Often deleting my work of HOURS (video editing is tedious but satisfying, as long as your work doesn't disappear). With video deadlines, and the emotional turmoil of losing my work (yes, turmoil--have you had it happen to you?), I was delighted to finally get an iMac.
Currently I am upgrading my skills to Adobe's PremierePro CS6 video editing software. PremierePro is not as intuitive as iMovie, but it takes customization to the next level. I've found that PremierePro is much better at taking multiple video files (especially from different camera angles) and seamlessly cuts them back and forth into each other.
Good luck as you market your book with a fabulous book trailer! Did you decide to use different video software? What did you like about it?