Autofill is worse then the first pick system that was in play for seasons 1 through 5.
FIrst pick: I prefer top but I'll play support or mid, I don't feel that confident about my jungling skills but I suck at ADC . Over 90% of the time I was able to get one of the positions I was fine with playing.
Season 6: I get to select 2 positions I want to play but if I put support as my secondary choice it will put me as support an excessively high amount of the time. This means that I have to change my secondary position to mid from support so I have a better chance of getting top resulting in queue times being longer due to a lack of people queuing up as support.
Autofill: I get to select 2 positions that I want but there is a good chance that I will be thrown into a position I know I am not good in and have a real chance of not being able to get someone to trade positions with me when this happens because they got one of their desired positions.