Given the background of the two characters i'd put my money on Gurney.
Feyd is a good fighter but he is overconfident and has little challenging combat experience (i'd not count prepared enemies and weaker enemies as effective combat training, merely adequate).
Remember that Feyd had trouble defeating an Atreides fighter in the arena and only won because he used a secret codeword which locked up the muscles of the Atreides fighter giving Feyd the opportunity to strike the death blow.
Gurney is a natural fighter and has been going up against Sardaukar, he managed to gain the respect of the Fremen (not easy to do) and while Feyd is physically in batter shape given that he's much younger Gurney has seen real battles and has much more experience.