I don’t think Frost has a set in stone “best” variation. She has a lot of good choices and what you pick is mostly preference or matchup dependent. The only hard rule I’d give is that you always run a combo extender in Mircoburst or Ice Auger.
After that you’re picking between
- Cryogenic Crown
- Quake/2nd extender
- Quake/Lunge
- Burrowing Auger
As someone who didn't use Ice Auger before and recently got clued in to the type of pressure it can offer in a lot of situations I think Ice Auger might be her ONLY OPTIMAL. There are a lot of combos of moves you can use for Frost for a lot of matchups after setting in Ice Auger and I think it comes down to 3 key differences.
Pressure based (Jax, Lao Etc)
Mixed Pressure and Zone (Sub, Kabal etc)
Zone (Cetrion, Skarlet etc)
These are all IMO
Pressure -> Ice Auger +Burrowing Auger
For the pressure matchup Ice Auger + Burrowing Auger is KEY. You lose a little bit of damage in some situations but overral you gain A TON of pressure that's safe once you learn which setup to use and when your opponent really wont be able to do much but accept having to block all your safe pressure especially if you keep your spacing tight. Start mixing in your throw game and it should be a breeze. Although there are exceptions like Liu Kang who are pressure monsters with the projectile game that can keep you out at the same time.
Mixed Pressure and Zone -> Ice Auger +Microburst + Icequake / Ice Auger + Microburst + Auger lunge
Against these matchups like Kabal, Sub, maybe even consider Noob in this category but I think he's a special case like Liu (Cheap ass characters) that can be considered to cover all areas, pressure and zone especially with his damage output. But in these matchups I like having Micro burst with auger for the little bit of extra damage and also the fact this allows you to get unbreakable damage as well if you hit your opponent with 344 after MB Microburst. This is key because in these matchups you have to make sure to output more damage in every confirm just in case they try to run away and zone, that way you have the life lead and you dont have to chase them. With Icequake as a 3rd option you can use this if the opponent has superior zoning to you and you need a way to get in. Best example is Sub-Zero. Trading with Ice Ball is never an option. Otherwise if you can play with Auger Lunge instead you now have a way to have an unbreakable combo that will pretty much corner carry across like 45 % of the map for easy pressure.
Zone -> Ice Auger + Icequake + Glaciel Calving
These matchups are the worst for me. I'm never the type to sit and zone so these matchups are hard for me and it took me awhile to figure out how to fight in these matches. But this is it right here. I found nothing else feels like I have a chance against zoners unless I run this. You can preemptive shield and try to respond with core discharge or Kryo stance to just check. Ice quake can get you in when you have a chance and it's pretty safe unless the opponent knows how to short hop the incoming low (Ice quake close range is an unsafe mid depending on the spacing anyone who does this is a nut), and once you're in use Ice Auger to setup your safe pressure and try to whiff punish or get a throw mix etc you get what I mean.
These are all subjective but This is in my experiances the best setups for her. I got 5 different variations the only other one being for Towers lol but these are my setups. I would say cryo crown can be used in the zone matchup but i think giving up Core discharge is a no no in any matchup. That bomb is too good, cant get projectile parried, and just destroys jumps .