How do you create the best Beyblade in the world using Beyblade metal masters and Beyblade metal fusion's Beyblades?

That depends of what Type you want.

For Attack types, going with a Meteo L-Drago, Lightning L-Drago or Galaxy / Bakushin (special promo Fusion Wheel) Pegasus / Striker / Capricorn / Aquario / Susanow (special promo Beyblade) is best.

For Defense, Rock, Counter or Grand with Aries, Leone, Orso, Zurafa, Scorpio or Cetus.

For Stamina, Burn, Inferno, Torch or Hades and Libra, Saggitario, Eagle, Pisces or Fireblaze.

The actual builds, however, are dependent upon the user. Some people like using some builds and other like the opposite. My favorite beyblade is Burn Libra GB145 ES (I think I have the parts right), a poweful Stamina type.