Old thread but I saw it got off topic.
Thongs overall cover your front while freeing up the back, reduce or hide panty lines.
Low rise can hide under your top pant line, but can possibly get pulled down easier while moving in the pants.
High Rise (waist) won't get pulled down by your pants, but they will more likely show when you bend over. (I picked her up from work and drove her around while her car was getting fixed) My sister's showed when she got out of car, prolly about 2-3 inches out of the top of the pants.
Overall, if you get them too small they might hurt up the behind. You wanna show em off; either take off your pants or get high waist and a shirt that won't cover your back when you bend over or get out of a car.
I personally only wear the low rise, find them comfy when all is set, and make sure to wipe your ass good otherwise it will get stained big time or a little every time you go. Washing stains out is never fun since you see what you did, and if you don't clean well and don't care and get a relationship - your partner(s) will see bad hygiene and its not attractive.