Parameter is for single selection whereas select option is for multiple selection. Parameter if you use and do not pass any value means in select statement it will search for a space value and if space is not there means it will fail. Meanwhile select-option low value is not passed means it will fetch all the records. So initial check is important based on requirement. this makes one difference.
Select-option with no interval and no extension, will give only low value in selection screen. if you double click on that you will get the pop-up with comparison operators.. <low value. > low value etc are still possible with this option.
In select option through user put input data in range and select option create internal table with option, low, high, sign. Parameter through can not provide input in range. It can't occupy memory.