Fate Stones or Blue Sylph?

[B4nsh33]

you will be able to upgrade sylphs later, how much will it cost or long will it take to level up fate? I think fate stones better, pets can be done later.

[Zhen_Hui]

Without a doubt, it has to be fate stones. There's going to be more sylphs being released in future, likely with better and stronger stats.

[symedia]

We will have other pets + these pets will have transformation into stronger ones:
apollo > apollo god
pan > medusa
and so on