This group contains the secondary characters. In recent anime episode, Sai and Baby 5 were featured and that had left some impression of them. It has been quite some time that we have seen the five selected people and I have to refresh my memory.
Monet - I have always remembered her wings and talons, and I call her "bird-lady".
Her most impressive performance was in Punk Hazard when she had battle exchanges with various Straw-hat members and Law.
She appeared to have taken more advantage with her body - having wings and talons. Being a harpy, she was able to fly and used her talons to attack her enemies. Besides that she also had the devil fruit ability, yuki yuki no mi, which gave her the ability to produce and manipulate snow. On an one-on-one combat, she probably might be able to win to a certain extent.
I'm looking at how she would fair with Baby 5 who is a medium-range fighter. Baby 5 is a "weapon-lady" as she has the buki buki no mi which allows her to transform herself to any weapon - blades, firearms, sickle or missiles. She is seen using firearms most of the time and lately in the anime, her encounter with Sai was pretty funny.
One of the disadvantages of Baby 5 is her personality - her belief system is all messed up. I feel that she is fortunate to have met Sai who is quite a gentleman who doesn't take advantage of her. Though Sai may have asked her to kill herself but it appears that he is saying it without any thought and thinking that people would not commit suicide just because one is told to do so. However much to his surprise, the one whom he has spoken to, takes his words seriously. For this reason, it may be a huge hinder to Baby 5 if she does not get her mind straight.
In this group, Sai has won over Baby 5, in the sense that it is not using physical strength over a fight but the heart. Sai has won over Baby 5's love or maybe I should say the other way round or simply both attract each other.
Sai seems like quite a good fighter especially when his grandpa has recognised and acknowledges his ability. He is pretty impressive with his Hasshoken and he also possesses Busoshoku Haki. I like the part where he fights his grandpa and win.
Boo isn't very impressive and he isn't at par with Sai. Though he participated in the tournament for mera mera no mi and was able to defeat a couple of opponents, but in the end, he was defeated by the Funk Brothers.
As for Gladius, he seems to be quite good in enduring attacks, probably a strong fighter even. He was able to defeat people like Kabu and Rampo, and withstood Luffy's 2nd gear attacks, but he didn't win against Cavendish and Bartolomeo. Perhaps it was not very fair for 1 vs 2 for him and hence he was defeated. But otherwise in one vs one, he probably may win.
In this group, I feel that Sai could win and the next one could be Gladius or Monet. I'm leaving Boo and Baby 5 out as they are not very impressive in my opinion. Baby 5 could be a candidate if she isn't so twisted in her thinking or else she would be a very good fighter. The only problem is when her opponent knows her weakness and takes advantage of her. If that is the case, it would be her downfall.
As for Boo, he is still in need of much training to at least win over his brother.
My first choice would be Sai and my second would be Gladius or Monet. But I'm leaning more to Monet in view of her loyalty to her master (Doflamingo). She was seen to be very responsible for her assignments (spying on Caesar, ensuring the tests were carried out properly and making sure that the children were "well-taken care of" (taking the pills constantly, no escaping, no rebelling, etc).
Monet could be considered as a patient person in the sense that she was "looking after" so many children who were constantly "crying to go home" and one of the kids even rebelled and tried to escape. For anyone, he or she could have gone crazy even with the noise of a kid. What's more with so many of them.
On the part of her loyalty, she was very determined to follow through whatever orders she was given by her master. For someone who could follow instructions so "diligently" or faithfully, she would be one who would carry out mission without fail. Though she might have failed in the fight due to her physical incapability but her spirit did not. She remained loyal till the end, upon her death.
With a spirit like Monet's, her loyalty, patience and endurance may be able to help her to excel to a higher level (if only she didn't lost to her stronger opponents like Law and Zoro).
The other one, Gladius, seems to be quite a short-tempered person. A strong head may not be good as sometimes a person's rage may actually hinder one's success. Of course not all the time. But if a person gets angry easily and acts without thinking, then the downfall may be forthcoming. Though Gladius is a good fighter, but if he can fight with a clear mind, perhaps he may be able to score some points in victory.
I guess that concludes my analysis.
Besides the 1 vs 1 battle, I'm thinking of having the contestants working in pairs - Sai and Baby 5, or Sai and Boo, or Monet and Baby 5 - and see how well they can play. I don't seem to see anywhere fit for Gladius.
I hope to see more people giving their opinion and sharing with us thoughts and ideas.
Cheers!