Ancalagon
Dusty Dragon
Really, the crazy thing about the spell is how well it scales. It starts at one tiny servant, but you get an additional two per level. Simply by upcasting it a single level you've tripled the power of this spell.
My friends, we have missed a portentous opportunity.
Based on this analysis, one would say that the "optimal" level to cast this spell is at level 4. This, on the surface, appears correct.
However, I had a dream last night, a vision (fever may have been involved). We were wrong, oh so wrong. The "best" spell slot level to cast this spell is not 4, it is 5? Why 5 you say? Because you get 5 servants? Why does this matter you say?
While this is not written in the book per say, I believe that once, as me, you have seen the light, you will realize that this clearly is the rule as intended, and that WotC will submit an errata at any moment now.
It's because the 5 tiny servants UNITE AND FORM VOLTRON!!!!
admit it - you see it now - the power, the BEAUTY!