yes, she does try, but her mistakes usually cost hundreds if not thousands of innocent people their lives. she's also slow to learn. She's not a particularly intelligent person i'm coming to think. I'll blame that on Viserys, and her ever-growing arrogance.
Jon on the other hand has shown to be very intelligent. I've mentioned on other threads about how highly i rate the intelligence of the Stark children, Jon included. He learns from his mistakes, and quickly. The situation is FAR less forgiving for him - he doesn't have thousands of people's lives to gamble with, whilst at the same time, he's gambling with the lives of the millions of people in westeros.
Stannis is doomed. of the baratheon boys, Renly was the best choice for a crown (by a LONG way).
Aegon, considering the Targaryan propensity for incest, makes perfect sense.
I personally believe he is who Varys and Jon Connington claim he is. Which, of course, makes him the RIGHTFUL heir to the Iron Throne. Not Dany, and most definitely not Jon (even if, and i do mean IF, R+L=J)