So who wins in a 1v1 against hisoka and each of the guards? This is a full on battle. No holds barred.
I personally think hisoka wins this easily. The royal guard really struggled against morel and his apprentice and nearly even lost. While hisoka had no problem at all defeating combat specialist hunters way above morel.
Killua also blitzed youpi while hisoka didn't remark about killua's speed at all. He was overlooking killua from this really high cliff and saw killua run with godspeed across this vast forest and yet he didn't say a single darn thing about it. That must meab hisoka is faster than killua.
So by comparison: royal guards are = morel who is < the hunters sent to take out ilumi needlemen who are < hisoka. Hisoka above the royal guard in every way. (sarcasm)