Street Trading and Grand Exchange may have the same purpose but one of them is better when it comes to making runescape gold.
Using of Street Vending and GE for runescape making
Grand Exchange is a place where you can buy and sell your rs items. However, grand exchange has a runescape gold price limit as well as selling slots for both free players and members. Though using GE is convenient especially when you’ll go back on your hunting activities, there are guild/party/players who are trying to compromise the runescape gold price of the rs items being sell by manipulating the price.
Street Trading is another way to make runescape gold, but its considered as “manual” selling as you have to be on your game to know if there is someone buys your rs items or someone inquires for the runescape gold price of your items.
Both can help you make runescape gold, but one is better than the others. Knowing the market value of your items for sale should be highly prioritized.