It's very simple, really...
I find it amusing that people, primarily marine players, continue to complain about how overpowered redemption is(even after the 2.01a devour nerf). Let me tell you guys something, if redemption is overpowered then Regen and Cara are godlike, in the hands of an experienced Onos. I'll explain why, and I'm speaking from experience both as and against an Onos...
First of all, it should be obvious that Redemption Onoses are the most fragile. They have nothing to help them take more shots like regen and cara do, and on top of that they effectively lose a chunk of their HP because they redeem after it hits that point. Regen onoses get some reasonable extra defense as they regen 45 hp per tick while they're being shot at, and have practically nothing to fear from electricity and unguarded turret farms. Carapace Onoses can just take more damage, for obvious reasons. Thus, Redemption Onoses achieve the least amount of destruction in a given time period.
Now the obvious reason people take Redemption is for the survivability. Redemption Onoses never die, they say. Let's ignore for the moment the fact that they actually do die(lag, concentrated HMG/shotty fire, nades, mine traps), shall we? The fact is that redemption Onoses sacrifice a great deal of usefulness for this little perk; they are redeemed before they even reach a structure or marine on a regular basis, and after 2.1 they'll have to stay alive long enough to gore someone to death instead of just devouring one. Redemption allows the Onos to play like a moron and still not lose his res investment, but generally he won't be able to destroy anything if he isn't careful not to get shot. A couple L3 LMGs can easily redeem an Onos before it reaches them, throw in some turrets and/or better weapons and they don't stand a chance.
Once an Onos is redeemed, he's left sitting back at his hive with double digit HP. At that point he has to fully refill his HP; it's not uncommon at all for the alien team to leave no D chambers at a hive, so the onos will often have to do this at 20hp per tick. After this he has to run all the way back to the marines(hope he has celerity). That's at least a minute or two of downtime every time he redeems. Then he'll be redeemed in 2-3 seconds the next time he attacks the base, and has to go through the whole process again.
Now let's compare this to the regen Onos. When the regen Onos retreats, he only has to run a room or two away from the base; if he's pursued he can either run further or just stomp and kill the marines out of their base. Once he's healed(fairly fast, at 45hp per) he goes right back in and does it again. The cara onos obviously has longer downtime; IMHO it's only really worth if you you get some DCs outside the base.
And then there's the last remaining issue: "Regen and cara onoses can be killed, omg!". Well, there are a couple answers to that. The first one is simple; learn how to leave the base before
you get killed. Knowing how much you can take while still having enough HP to make it away is a skill all aliens should have, and Onoses are no exception. You can never be too safe; set yourself an objective before going into the base(devour an HA, destroy a turret, whatever) and once you accomplish it run back out regardless of your HP. Remember that the less damage you take the faster you'll be able to go back in, so it never hurts to retreat early. Just because you're an onos doesn't mean you need to take all the bullets; even if you can't hide fully behind a structure like a skulk can, standing behind it and crouching while goring it will still block some bullets. How much damage you want to take before leaving is up to you, just try to leave some room for unexpected circumstances like a marine outside the base. If you're lucky and have 3 hives, just charge in, cause as much carnage as possible and speed out the door when the energy gets low. In the event that you do die, regen/cara onoses get more kills than redemption ones and if you've been playing well you should have had 100 res for some time already.
In summary, if a base is so extremely well defended that a regen Onos can't possibly survive in it, then a redemption Onos can't possibly stay in there long enough to destroy anything. Those of you Onoses who refuse to use anything but Redemption, try Regen for a change and maybe you'll be pleasantly surprised. Just remember that regen/cara onoses take brains and skill to play effectively, just like every other alien species. All you have to do is learn how to keep them alive and break the habit of suicide rushing, and you'll find they're basically superior.
That was really long. Hopefully I won't have to argue this in the other threads anymore