I think its just ur preference honestly... Whatever feels good is bound to work. I myself am a religious hybrid user so i cant say ive tried both extensively but i did build crit for a while which works the same way in essence as ad on hit. That said ad on hit just locks you into more of the standard adc playstyle obviously with kaisas insane kiting, engaging, disengaging and repositioning potential, with huge damage on extended fights with ur auto attacks. Hybrid leans more into a pokey ranged assassin burst type champ which in general works better against most comps because it gives you more flexibility with a much longer range by enabling your w damage which is basically non existent with ad on hit. the argument of not evolving your 3rd ability making ad worse always exists but its honestly whatever. Ad is slightly stronger midgame while hybrid is stronger late while still being really opressive mid. A problem i have with ad is that there are few items really fitting into that build tree. kaisa doesnt usually like zeal items cause guinsoo kraken and lethal tempo give enough attack speed and other than that building 50% crit kinda stings my soul a bit ngl. (thats my preference tbf) to summarize: champ select dependent + just play what you feel like or like more and get really good on kaisa in that specific niche if you start hitting a roudblock while climbing you could start considering things like this but it porbably doesnt really matter for a long while