Fastest Way to Charge Zarya's Ultimate

I've been seeing a lot more of this lately in competitive pro play and the pro scene; Zarya players get their ultimates extremely quickly. I understand that their skill and accuracy plays into it quite a bit, but I'm not too shabby as Zarya, and I feel like I earn ult much more slowly.

Is it more beneficial to charge ult by using her secondary fire? Does it have the potential to earn more than by just using the beam?

In Overwatch your ultimate ability is primarily charged through damage dealt and time. Certain heroes have exceptions, namely support heroes that get charge for healing or heroes that can self heal, but Zarya is not one of them.

Zarya's ultimate is only charged through damage dealt and time. In regards to what attack to use, Zarya's lob ability does 45 damage per shot (according to the wiki) while the beam does 95 per second when Zarya is at 0 energy.

Since damage dealt is one of the main ways to get charge, you would get fastest charge with the beam since it does more damage per second.

Zarya's core game mechanic is keeping her energy level charged through the use of well-timed shields. The higher her energy, the more damage she deals. As is the case with all heroes, the more damage you apply to enemies, the faster your ult charges. Thus, the key to playing Zarya well is knowing (and reacting to) the best time to shield both yourself and your allies.

The reason pro players seem to charge their ults so quickly is because they keep their average energy level higher than the typical Zarya player. They are able to read the flow of battle and react quickly when (for example) they see their support Mercy get hooked by an enemy Roadhog. Not only does this save the support, but it also gives Zarya a 40% boost to her energy (and damage)!

As for the most efficient method of damage to charge her ult, that depends on the situation. When attacking single targets, her beam is definitely stronger - it does twice the damage per second that her lobbed charge does (95 dps vs 45 dps at 0 charge), assuming your tracking is adequate. However, because the lobbed charge does splash damage, it is more effective to use the lobbed charge if there are 3 or more people grouped up together (95 dps x one enemy vs 45 dps x 3 enemies = 135 dps).