Who do i use my seeds on i already have argon max who i was told was thé best for your first one
#Seed use
zenith wasp
shadow abyss
Pick your favorite Champion, really.
Stat seeds give a relatively small boost all things considered so it's not hugely important to use them as efficiently as possible. The game also gives them out like candy so you will always have more.
That said, it's generally advised to stick with Champions for this first. Your heroes are very likely going to be temporary. It's normal and honestly a good idea to not try and optimize your heroes early on. You'll always have your Champions however, so investing in them is never a bad idea.