* かかってこい！(Kakka te koi!) This is a very common and strong way to say "Bring it on!" It's aggressive and challenging. Literally, it means "Come on and attack!"
* やってこい！(Yatte koi!) Similar to かかってこい!, this means "Bring it on!" or "Do your best!" It's also challenging but slightly less aggressive.
* 来い！(Koi!) This is a shorter, more concise version, simply meaning "Come!" It's still challenging but less verbose.
* 挑戦を受け入れる！(Chōsen o ukeireru!) This is a more formal and polite way of saying "I accept your challenge!" It's less aggressive and more of a confident acceptance.
* 受けて立つ！(Ukete tatsu!) Similar to 挑戦を受け入れる!, this means "I'll take it on!" or "I'll accept the challenge!" It carries a sense of readiness and resolve.
The best choice will depend on your situation. For most casual situations, かかってこい! or やってこい! are good choices. For more formal situations, 挑戦を受け入れる! or 受けて立つ! would be more appropriate.