I chose iGoogle but only because I have already been using iGoogle for a few years! I love iGoogle because everything is customizable which is convienent. I know once I started college I wanted different widgets on my homepage and changing it was not a problem. I use Google for pretty much everything so I was thrilled to share my positive experience with it on my blog!
Again, I use Google Calendar all thee time! I am a proud and happy owner of an iPad 2 which links with Google products. I use GoogCal (which is what the app shows up like) and have my appointments and deadlines emailed to me. Using this is SO EASY and it makes scrap paper lists a thing of the past!
I have an app on my iPad that is called Reminders which is basically like a To Do list on my iPad. I really like using it so I doubt I would use an online tool. However, I did try out Remember the Mile and I liked how it broke down different categories. That's very helpful! I have signed up for an account so I will let you know if I end up using it!
I would recommend Google Calendar the most. The best part is the reminder email! It automatically sends and that keeps you from having to constantly sign in and check for deadlines. I love my Google account! Use Google!!!