Warning, Beyblade jargon ahead, pls click off if u are not a blader. Disclaimer:I have not used any of these combos myself. This is going by what I see on the wiki and Youtube. Constructive criticism is much appreciated These are bey combos I think represent each yk character.
Kengo Benimaru[]
This was easy. If Beni's primary ability is a sword, there is only 1 layer to use: Sieg Xcalibur. I mean, both are red, and if I use Buster, the gimmick will get in the way. I will use the Blitz Disc as 1 and Xcalibur combos are overused and Blitz's triangular shape should compensate for the imbalance Xcalibur beys always suffer from. I think I will use Xtreme/Xtreme' as he is a straight-up attacker.
Junior[]
Since this is his most used shadowside mode, I will use Flare Dragon to represent it. I will keep the Around Disc but the Driver I will use Trans/Trans' as Junior, being a shapeshifter, can change abilities based on what he changes into, and i used Trans as it is the only mode change driver with consistent performance.(*cough*Zeta*Cough*).
Harry[]
I have no info to go about Harry except that he shoots needles(but that's not a reason for using Phoenix or Bullet)that make people morose. So, I did the next best thing:colour scheme. Harry is classified as grey, so I think I will use Alter Chronos(in defense mode, attack mode is just so bad). I will use Hurricane as it is spiky and the driver will be needle as a nod to his prickly powers.
Reversa[]
The only info I have is that this yo kai makes you unpredictable, so I have to use Judgement Joker's stock combo as the entire bey is unpredictable. Enough Said.