Nature Runes
Although you won't receive multiple Nature runes per pure essence, you will still make more money running Nature runes than running Air runes. Pure essence currently cost 119 gp each and Natures cost 230 gp each.
Cost: 28 pure essence x 119 gp = 3,332
Money Earned: 28 Nature runes x 230 gp = 6,440
Profit per Trip: 6,440 - 3,332 = 3,108 gp per trip
You can see that running Nature runes is more profitable, but it initially costs more, too. 3,108 gb per trip isn't too bad, but Laws still can make you more money. So the question is: Why run Natures when you can make more with Laws? Many people done like to run all the way to Port Sarim, then take a boat, then run again until you hit the Law rune altar, so they might go with the easier Nature rune running. Other people may be getting Nature runes to use for High Alchemy, so it all depends.
Law Runes
The most profitable runes are Law Runes. You still only get 1 Law for 1 pure essence, but Law runes cost 283 gp each.
Cost: 28 pure essence x 119 gp = 3,332 (Note: The same as Nature runes.)
Money Earned: 28 Law runes x 283 gp = 7,924 gp
Profit per Trip: 7,924 - 3,332 = 4,592 gp per trip
Hopefully, you can see that there is an ample amount of profit able to be made in minutes of running around Runescape. Law runes are your best bet for making quick, fast money, but don't forget about Natures or Airs, because those are needed to gain initial wealth or to get other levels up fast. Use this rune running guide to your advantage and start making money on Runescape now! Time is money, and money is everything in Runescape. Hopefully this will be a way you can use to get your first 100k gp, 1 million gp, or 100 million gp.