American Revolution wins out because it lasted longer (1770-1865) whereas the French Revolution only lasted a fraction of the time (1789-1815).
Although by this long count, the French Revolution arguably lasted until 1871, when the last hope for a restored monarchy died.

I have never seen it argued anywhere ever in any historical work that the American Revolution lasted beyond the Treaty of Paris, let alone another century.
Though we must also look to the fact that one reason the French monarchy and state at the time were in such financial troubles was partly due to France's involvement in the American Revolution. So by effect, we could say that without the American Revolution, financial troubles would probably not have been as stressed as they were in OTL history and the monarchy could probably hold onto power for a while longer.
French finances were in... less than ideal shape before intervening in the American Revolutionary War. While this involvement did hurt finances even more, it is quite possible that the French monarchy could have survived if the 1780s had gone a bit better for them.
...and unable to just stop, but no one had the necessary political will to break the nobility interest's power and reform the opaque finances: the king would appoint ambitious reformers from outside the nobility like Necker, but wasn't actually going to do anything to put their plans into action.
You don't know how glad I am to see mention of Necker on this board - in my extensive research into this era, I have come to the conclusion that he was one of the few men with the will, political clout, and actual financial capability to enact real reform. While arguably his over reliance on loans was one of the causes of the eventual financial meltdown, from what I understand Necker was just borrowing to retain solvency until he could reform the financial system so it could stand up on its own. He came pretty close to success, too- his one mistake was resigning before the death of Maurepas. If Necker had managed to outlast his only major political opponent, he could have cemented his office and continued to overhaul the French monarchy's financial system.
You certainly could avoid the revolution, but you'd really want a frugal, practical, decisive man in Versailles, a William IV or Louis XVIII. With Louis XIV, I can't see anything being achieved before the money runs out.
Do you mean Louis XVI? He wanted reform as well, more than anyone else in France. And reform did come, but the way it was handled was disastrous. A line can be traced from the "May edicts" disbanding the
Parlements to the Estates-General, and from there to the more radical revolution.