I've been researching and testing this for two months. Leon Crest 4-55 / 4-50 Under Needle was the best out of all of them.
Leon Crest is unique because it is essentially a CX blade (metal on top, plastic underneath) without the weight of a CX blade, so it has all of the drawbacks of being top-heavy and low stamina without the benefits of a blade heavy enough to make some weird anti-meta attack or mobile defense work, nor does it have a smooth or round enough shape to glance off attacks like Ghost Circle or Shinobi Shadow on Wall Ball. It also tilts over very often, so a tall height is basically a death sentence for it. The one saving grace that it has is that the plastic blade actually does protect the ratchet, so it is free to use the widely available 4-55 and partially negate its bad burst resistance. 7-60 does add more weight, but I wanted the lower height and more even weight distribution of 4-55. Under Needle is currently the best bit due to its low height and stability, but I fully expect to replace it with Under Ball, Under Orb or any other low-height bit variants once they get released.
Leon Crest 4-55 UN vs Shark Scale 1-70 LR
5 wins (5 spin finishes), 15 losses (6 spin finishes, 5 over finishes, 1 burst finish, 3 xtreme finishes)
Remarks: As is expected of Shark's attacking quality and late-game stamina, Leon Crest gets rushed down far too often, so it conceded a lot of spin finishes to a nominal attack type. Under Needle, being a low friction bit, has difficulty resisting knock outs. If TT ever releases an Under Wall Ball bit, this match would have a much different outcome.
Leon Crest 4-55 UN vs Phoenix Wing 3-60 R
13 wins (12 spin finishes, 1 burst finish), 7 losses (2 spin finishes, 3 over finishes, 2 xtreme finishes)
Remarks: Leon Crest itself does have the uncanny ability of eating a direct hit, slamming into a wall and surviving. Again, a better bit would've made all the difference here and denied Phoenix the 3 over finishes and 2 xtreme finishes it has and turning the match into a rout.
Leon Crest 4-55 UN vs Aero Pegasus 3-60 R
4 wins (3 spin finishes, 1 burst finish), 16 losses (11 spin finishes, 2 over finishes, 1 burst finish, 2 xtreme finishes)
Remarks: Against Aero, a better Phoenix Wing in terms of attack and stamina, Leon Crest has no good answer to it. The amount of conceded spin finishes exposes Crest's stamina weakness hard, but it could still theoretically salvage the 2 over finishes and 2 xtreme finishes if given a better defensive bit. Under Wall Ball does not exist just yet, but I think a heavily worn RA could do the trick. However, I don't see a reason to use the worn RA on Crest if you actually have one that's tournament legal.