What's the best thing to get to get rid of stretch marks?

Avoidance. Unfortunately, the best way to get rid of a stretch mark is to not get one in the first place.
Help stretch marks. Microdermabrasion creams and retinoic acid products can help regenerate some collagen. If they are red, pulsed dye laser can help remove that color and shrink them down. Whisper and fractional co2 lasers can sand the skin to make the normal and stretch-mark skin look more like each other. Nothing can erase them.
Stretch marks. There are treatments available, particularly with lasers, which can help improve stretch marks, however, no treatment can yet make a stretch mark go all the way back to looking like totally normal skin.