I have Best Berserkers whom should I roll for?

Quetzalcoatl is a Rider. It actually makes no sense to compare her to two Berserkers, even if the comparing factor is how much damage they deal. These are two different classes entirely, and there is much more to consider. You're overlooking class advantage, which niche each servant fills, their skills and how they affect your team, class-specific attributes, etc. And believe me, these change everything.

While you technically CAN make your way through the entire game smashing things up with your berserkers, let's be honest, where's the fun in that? The game has over a hundred servants for you to use, each and every single one with something unique to offer. So why limit yourself to two of them?

Also, do keep in mind that there will be moments where using Berserkers isn't a good idea. For example, there are enemies who can damage your entire team at once, and naturally, Berserkers will suffer more than anyone from that since, well, it's either obliterate of be obliterated with them. This, among many other reasons is why class advantage is so important. NEVER hesitate to have strong servants for each class.

Every 5-star servant hits hard, that's a fact. They aren't 5-star for no reason. Even if they are terrible servants overall, their high stats alone are more than enough reason to invest in them. Quetz is no exception to that. She IS strong, probably even more than you might think. Her ridiculously high stats aside, she can offer a lot to your team with her skillset, from teamwide attack boost to targetable guts. So, not only she is a 'powerful hitter', but she can also be very helpful to your team. Also, as you mentioned, she is waifu. Isn't that more than enough reason to summon her?

I gave a quick look into your roster and the first thing I noticed is that you lack a strong Rider. Martha isn't bad, but she isn't amazing either. I'm sure you noticed she doesn't hit hard, while Quetz will 20k a nigga with a single Buster card. So yes, she would definitely give a LOT of help to your roster.

There is no such thing as having too many strong servants. Raikou, Cu alter and Herc are monsters, but they aren't the only ones that can be useful to you. So don't be afraid to want and try your hand rolling for them. You WANT her, so why would you not go for her?

Honestly, there are so many servants that could add depth and strength to your roster that it's pointless to try and list them. Which is more than enough reason for you to give your berserkers some rest and try out all the other things this game has to offer, don't you think?

Sorry for the long text, I hope I was of any help to you.

Well. I think if u are lacking of strong rider, Quetzlcoat is really good.
Berserkers are natural to destory enemy typically u already have best berserkers, but in most cases they are pretty fragile in the future. Even Cu, facing some aoe and buff-removing boss are quite frustrating. Also in most cases their role is to elimate mobs rather than boss fight (especially inthe future), OR replace 1-2 teammember of assassin/caster team due to their low attack modifier and status, lack of buster card, etc. For instance, Waver-Raikou-Cu team is pretty powerful against any assassin, even finish the battle before Assassins' short np gauge fulled. But not really can substitute the role of rider, especially Quetzlcoatl or Ozy level.

Overall, imo, if u ask whether to roll Medb, or keet Cu or Raikou? I will hesitate. But Quetzalcoatl is another story. Also, rider-caster support-berserker (no matter raikou or cu) is also a very versitile critical team to face mamy circumstances.

It's a bad habit to run zerks instead of class advantage. I'm just gonna leave it at that.

Besides, we don't know your roster at all.