In terms of development speed, which would be faster: webforms or mvc?
WebForms can be a little faster to develop since it's a lot of R.A.D. development. Long term however, you will regret not separating your concerns. Keeping a separation of concerns may take longer but is a lot easier to maintain after the fact.
How about out-of-box performance between the two?
MVC will perform better since there is no "extras" being passed between the controller and the View. you only pass what's necessary (IE: no ViewState)
In a long term which would be easier to maintain?
Back to what I mentioned above. Keeping a separation of concerns may take longer but is a lot easier to maintain after the fact.