Other things to consider are:
1. how likely are you to switch carriers at the end of your contract? if you think you won't like VZW's phone selection or service, then a 1-year deal might be the way to go.
2. what will be your base rate for a calling plan? if it is $60 or higher, then you get an annual upgrade for a new phone anyway. just keep in mind using the annual upgrade renews your deal for another 2 years. but if the phone selections keep improving and you like the service from VZW, a 2 year deal is probably just as good as a 1 year (maybe better).