Which Gathering skill should I level to make some decent money quickly?

Let me put that into numbers since decent likely means different things to different people, I have 40k gil and 5 level 50s so I am dirt poor.

I don't wanna use my DoM or DoW to make money I have enough to do on them just a gatherer to mess around on for an hour or so after RL work.

1) So with that explained and back story please give me some advice Fishing / Mining / Botany which one should I level to play casually for an hour or two at night in order to make a few hundred k gil.

2) What should I be gathering with the suggested class to make this gil?

3) How effective is it in your opinion? I have had Petrified log on AH for a week and every single day I check I am undercut and mine never sell I don't want that situation.

Thank you