use your own common sense dude, buy SSD interface type according to your laptops specification, if your laptop got sata II interface than what sata III gonna do good? it will only utilize sata II speed. you are only good if laptop hdd interface and ssd are both sata III.
besides interface first and foremost thing to look for is SSD tech.
MLC = slower and short life span hence cheaper.
SLC = faster and longer lifespan hence expensive.