I am moving to the iPhone 4S once it arrives. Currently I am an Android user - use Google's contacts, Gmail and Calendar.

What is the best way to ensure my contacts are backed up when I begin to use my iPhone 4S?
Should I move everything over to my MobileMe/iCloud account or should I use GMail as an exchange account (aka setup GMail via an exchange account) or just click GMail when setting up the email?

What are the Pros/Cons?

Please advise.