lol man this is funny. Just because I like to instigate things, here's what I think:
Timer:
~ You know when to go and reaction time is completely out of the equation. This system might work if everyone in the room is legit but even then it is soooooo easy to take off a tenth of a second early and thats all it takes to win the race. Also it is possible that the timer is different for some people up to a full second. Seen this in many rooms.
Tree:
~ IMO closest to reality. Reaction time of the driver AND quality o his tune decide if he will beat his opponent. People complain that you take off late because there is no "yellow light". Though I don't prefer it, I see many people turn on their lights or turn their wheels before ghosting. Yes there can be ghost lag but most of the time your opponent realizes it and reverses back to the starting line... at Indy at least.
Bottom line I never knew veteran draggers use timer. I only use it when me and one other person is on the track and there is no other alternative. There is a reason that in real life drags they have a light instead of a huge timer