Heels on the floor for me every time - it does not take a nanosecond to get full brakes on if necessary I can assure you.
I have seen too many pilots inadvertently applying just a little bit of brake on take-off with their feet off the floor without realising it.
Apart from lengthening the TORR this practice does nothing for brake and tyre wear and raises brake temperatures (especially with carbon brakes) which scarcely helps in the event of an abandoned take-off.