hi,
I would always have some level of positive feedback when using the LM311 comparator.
This will prevent 'chatter' at the switching threshold. ie: rapid high/lows at the output at the threshold input switching level.
Never had an occasion to use negative feedback with a LM311.
E
There is an extremely low frequency amplifier circuit that uses a comparator with negative feedback as an opamp and it has frequency compensation with a fairly high value capacitor on its output to ground.