I prefer coiled since it's usually shorter and easier if you're close to your source (ie computer or phone/ipod if mobile). Don't think it really matters much though, not like its gonna change the sound quality or anything. Haven't tried both the M50 variations myself, but there's tons of threads about it on the internet.
Also off topic, you might want to look at other headpohnes from the m50. They are really popular and not bad but for gaming there's really not much reason to go for them over open back phones (ad700, various sennheisers, etc). Might as well go for soundstage if you can.
http://www.head-fi.org/t/459443/audio-technica-ath-m50-straight-vs-coiled
http://www.head-fi.org/t/628517/ath-m50-or-ath-m50s-i-know-i-know-just-hear-me-out
http://www.head-fi.org/t/575394/ath-m50-coiled-or-straight-cable