I'd say it just depends on what skills you'd like to train. Natures are probably slightly more profitable and offer a better margin if you stick with them to 91+ runecrafting, though.
Both are pretty much <month autobans, but if you're dead set on it then RC is more profitable if we're talking gold itself. GDK is better in the long run since you can sell the account when you're done as a staker/main/etc.
You only get one lap in life, make it a flying one
If you aren't botting, then go green dragons. It's probably more enjoyable and with whip + 90str, you'll be killing them very fast. Use glories to bank via Edgeville and kill west dragons.