That's a lot to choose from, and actually, given the way you write your stories, there are in fact more plot twists than just those. But sticking to what you've listed, I shall put my reply in a spoiler, so as not to spoil your spoiler (if you see what I mean)
Of the 3 in LF, I'd put the meteor at the top, partly because it was so unexpected and the consequences potentially so negative. There had already been quite a number of hints etc., ahead of Sandy's abduction for that to be a real surprise. I'd never actually thought of the GC hiding in the rubbish bin as being that much of a plot twist. Much more was the need to beat the other 2 to get out.
MM3 and Jeanne - yup, quite unexpected and a great way to solve the dilemma. Of the MM4 suggestions, burning down the Bear's house was the best.
In Asguaard both the framing of Glen and Rayanne becoming the Stone of Soul were great twists, difficult to choose between them.
Obviously in MC and TBOL the twists were the only ones. In Sylia, definitely the fact that the pets took over.
Now to try and pick the best - almost impossible
Having sat and stared at the screen for a bit, I'm going to go for Rayanne in Asguaard. But really it's very hard to say that one is better than another.
Actually, it's just as well I put it in a spoiler, as otherwise it would have been a bit of a wall of text.
Good topic.