I would prefer the straight salary...
I am currently on the salary+flight pay and it really digs into you when your sitting at home realizing that you're not making money. Where as with salary, when you are home you really don't need to worry about anything.
Also, make sure the 300/day is per duty day, not per day you fly. Ours is only days we fly... so if you fly somewhere and sit two days, fly back, you only get the 2 days of flight pay, not 4.