Pandora is the hardest to get smooth.
L-cuts are also hard to get smooth.
Hardest move to get down for me is the Eye-Cut but then again not sure if its really a flourish.
If it's not a flourish, what is it? Flourishes pretty much equal XCM moves, if that's what you meant.... It's a display but can be categorized under an XCM move or a flourish, however I think flourishes refer specifically to moves done in conjunction to magic. See here for additional info to clarify: http://www.proxcm.com/beginners.htm