This is totally up to you and your opinions...
TT Beys I have already:
Vanish Fafnir
Union Achilles
Lucifer The End
Limit break dx set
Geist Fafnir

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Overdrive Set or Sparking Triple Booster Set, get Overdrive Set first as it is worth it, then later get STB

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I will forever make Top Gun references

definitely get the overdrive set because it is everything you need weather you like a defensive beyblade, stamina beyblade or an attack beyblade and it is a higher price than most sets, but is is extremely worth it.