Pre-timeskip, Kidd was probably a little stronger than Gear 2nd Sabaody Luffy.
Post-timeskip, he's featless, though given how he's being portrayed as a potential rival for Luffy, I'd say it wouldn't make much sense for him to be fodder to Luffy. Kaidou kept him alive, which may hint he sees potential in him. Via-hype/speculation, he's probably at least stronger than Gear 2nd Luffy, though saying anymore without evidence is a stretch.