Shadow Claw and Shadow Ball have the same speed priority, the reason you probably think it is faster is because a faster pokemon used Shadow Claw.
Also Gengar should never carry Shadow Claw over Shadow Ball, as it's attack is inferior, and as such, Shadow Claw is a physical move (working off attack stat) and Shadow Ball is a special move (working off special stat)
As for WiFi, Gengar normally dies in one hit, so Rest + Sleep Talk isn't a good idea to begin with, and you were probably horribly outspeed due to the fact that you probably haven't EV trained your Gengar.
As such, check
http://www.pokecommunity.com/showthread.php?t=123757 for all information on EVs and IVs and such to make your pokemon better
Anyway a good Gengar moveset is this
[email protected] Lens/Life Orb
Timid Nature
EVs: 252 Spd, 252 Sp Atk, 6 HP
-Shadow Ball
-Thunderbolt/Energy Ball
-Hypnosis
-Focus Blast
Covers alot of ground, one of the standard Gengar sets, or if you prefer pure power
[email protected] Specs
Timid Nature
EVs: 252 Spd, 252 Sp Atk, 6 HP
-Shadow Ball
-Thunderbolt
-Energy Ball
-Focus Blast/Hidden Power (Fight)
Choice Specs gives his special attack a 1.5x boost, but limits you to one attack before switching out
P. S. Saying you don't like stalling an opponent, yet using a Sleep Talker is a bit ironic
__________________
Angelic Diablo's
PokePet

Slicer the level 46 Scyther!