First: They are different factions. Who you're doing content with is more important than your racial 100% of the time. If you don't know, it's not important.
Second: Outside of stealth classes (especially Sub Rogues) abusing Shadowmeld, basically all racials are balanced within a couple hundred DPS of each other in most cases. It's not significant enough to worry about; you should be whatever race you resonate with.
Third: The actual DPS difference of the choice between the two races will come down to player skill and fight. Popping Berserking during a burst phase or stacking it with other cooldowns will cause it to pull ahead, but Worgen's darkflight can also be a DPS gain on movement heavy fights.