50:50
Fox's better stages.
Final Destination
Smashville
Rainbow Cruise
Halberd
Lylat
Port Town
Snake's better stages
Battlefield
Yoshi's island
Delfino
Frigrate
Norfair
Luigi's Mansion
Yeah yeah Snake can't Grenade cuz Fox Blows them up, well, no smart Snake would stand there and try. Still, it's good to void one of his options, but Snake can draw his nades during a jump. Don't take him to stages with a lot of platforms, Smashville is fine, because that one platform is not a worry as long as you pay attention to it. Yoshi's Island gives Snake a plethora of traps to set due to the rotating platform and awkward stage slopes. Fox can camp and dance, but Snake has range and power. Because of Fox's horrible vertical knockback resistance, up tilt is no happy for Fox, neither is down tilt.
Snake, on the other hand has great vertical knockback resistance (second only to DeDeDe) and is a DI guy so yeah, he dies from up smash much later than average. Fortunately, Snake can get himself trapped in a self damaging loop if he recovers wrong. Cypher > C4 > repeat, and he has no choice but to keep going. It's easy to get Snake in this loop by down smashing him around 20-50% near the edge of a stage (try it!).
Uh, if Snake CPs Battlefield, don't use Fox. It's horrible.