i would say it is dependent on what type of trading you are doing. if you are scalping size for nickels, then both are equally important as you don't want slippage on either execution's end.
if you are looking to hold for longer periods and price moves, then having the discipline to your planned exits is more important as a few pennies here or there on entry don't matter as much. however, if it is a matter of deciding to go long or short, then the entry direction is just as important as the exit.
if you are looking to hold for longer periods and price moves, then having the discipline to your planned exits is more important as a few pennies here or there on entry don't matter as much. however, if it is a matter of deciding to go long or short, then the entry direction is just as important as the exit.