Well, the insane zerker DPS you're reading about is tied directly to their Dicho ability, which means you get to use it once every 60 seconds. If you're burning a single mob or need to get one dead quickly so you can relax and take on another, then fine, but if you're looking for sustained burns a zerker isn't the end-all, be-all that it might appear. Now, they're f'n awesome (I love mine), but for a specific mission or something you'd have to manage when you burn the house down and when you're "just good."
Overall, I'd probably guess that a zerker is more dps over time than a beastlord (comparably geared). So, if you want to keep your group makeup and are just asking about zerker vs. beastlord, then zerker is better, but you lose some utility.