On a trike gear I like slight negative. When you're flairing in and the mains touch as as speed bleeds off you tip forward and the flight is over as the wing loses lift. You can also build up ground speed in preparation to rotation and take-off.

Trainers that have been slapped down a few times get overly squat at the mains and have too much positive incedence. Thay take off prematurely and bounce in as the wing is always trying to lift.