From what we've seen I think Kurapika edges it out.
From what I think we're going to see from current Kurapika, he'll stomp. Emperor's Time has the potential to be massively broken - he can develop master, high-end techniques in every Nen Type at use them at 100% efficiency. He already did it once for Enhancement/Holy Chain, I expect since we last saw him he's developed new techniques.
Anyway, as for the fight.
Kurapika can use EVERYTHING in his arsenal on Killua besides Chain Jail - that's the only power restricted to the troupe. I think with Holy Chain Kurapika can outlast Godspeed and then kill him with Judgement Chain or 100% Enhanced Punches.
He paralyzed Youpi and was hitting him like a punching bag
He was said to basically teleport by the ants
He disintegrated Poufs face instantly
Nothing can harm in with Godspeed
He can bench like 164 tons, he can flick Kurapika to the moon
I'd have to say Killua, he has more raw skill, at that age being able to measure himself to Kurapika is amazing. To top it off, his speed is amazing, with the yoyo's he has a counter to Kurapika's chains, to top it off he has lightning now.
Im not so sure about Killua winning, Kurapika has what it takes to outlast Killua in godspeed mode, all he has to do is take a few blows and heal with emperor time once godspeed runs out then finish Killua off there. As much as I like Killua I simply cannot brush off Kurapika's skill in nen either.
This might sound stupid, but I honestly think the fact that he has his yoyo's or not greatly effect the fight. He was quite fast and precise with them. Also, another thing which can give Killua the age is his stealth, he can most likely keep out of Killua's eye sight and constantly surprise him until Kurapika is tired or confuse him with illusions, (Rhythm Echo is the name of the ability). And to top it off Killua has a high pain resistance.