Which to ultra evolve first?

So I am looking for something to help me in UC and PVP. 

My current legendary’s ready to Ultra evolve are. 

Tridrake

Atrasar

Valzaguard

Necrowing

Cryowyrm

drakotron

nighthorse

pyrrophim (have serapheon so kind of redundant?)

gigarock (already had The GF- so kind of redundant)

Bovolk

Drakuleus

Galliovern

Pengbot

Coalknight

Ziberos

Freeznix

I was thinking that the next one I would do is Bovolk for HG and thought this one would help with getting a quick +4 kill with deathmatch/superblaze all with team turn and give turn.  Thought this would help a lot in UC? what do you think? 

I was thinking then to upgrade drakuleus and galliovern which would pair well with bovolk with hp share, purify, and infinite lifeflip?

I find Ziberos actually pretty weak it doesn’t even one shot some SE monsters? does anyone else think that this one isnt worth upgrading?  Its pretty bad for a LE legendary/first one. 

Do you have any other suggestions? Also, I have currently removed doomengine from my teams but is he worth having in UC team? 

Other Fully evolved leg include Terrordragon, bane, midasdragon, The godFather, Rexotyrant, Serapheon, Soulstealer, Mechaviathan, Stromloch, nightrider, Omegasdragon

Bov does not have HG, but yea evolve him he is very usefull, zib is an amazing legend but for pvp, kind of useless in pve.
Im guessing pengbot could help too.
The shocking entrance guys too, they could also help.

Do not ultra bov, he only gets poison revenge which is most time useless… you only need him for his death match and it’s better at 8 cost usually

That’s the mistake I made too. Not to mention that if the opponant manages to kill Bovolcus after Deathmatch is used it really screws you over if you have someone with Bloodfury to set up.

Well darn I was thinking he got HG. So is he still good for UC? What is the best way to use him?