BY FAR! At least when Zelena realizes a romance she's in is bad, she gets out of it and does what needs to be done. Belle is constantly going back to Rumple after the terrible things he's done to her and others, especially since he says he's not going to change. He's always choosing power over her and she never seems to get the point that she should just GIVE UP and move on with her life (But stay away from Will Scarlet, he belongs with Anastasia Tremaine). Belle was definitely the last person who should've gave Zelena advice on what to do about her love life, especially since Belle knew it was Hades who loved Zelena.

As you said, she knew when to quit it. I mean the dude lied to her and murdered her sisters' man.

Belle just makes the same mistake over and over again.

At least Belle did stand up to Rumplestilskin occasionally. It took Hades trying to kill her sister for Zelena to do anything of the sort, when killing him became the only way for her to save Regina.