Benefit of the doubt goes to the bowler, they need to see the heel clearly first touch the ground on/in front of the line. Without slow-mo camera it's not ideal.
In the case where there is an out as the result of an appeal, if there is any doubt, it should go to the batsman.
The issue here is that international umpires have stopped looking for no-balls, and revert to the TV replay in the case of an appeal. This was confirmed by one of the ICC umpiring board in the Ashes this summer, and the reason is that they don't want to look stupid if they inadvertently call a no-ball that isn't. There were a lot of uncalled no-balls in the summer, and frankly, it isn't good enough.