dnd 5th – Which backup jets are the lowest level enemies most likely to succeed / fail?

Related to this question: What types of damage are the most resistant and the least resistant?

I'm wondering which backups throw down the low-level enemies who have the best chance of succeeding and / or failing in meetings.

For example, if I had the choice between six spells to use against a random enemy whose statistics I do not know, and whose each spell has a single save throw, which spell comes out most likely to fail at cause of a saving throw? Which one has the best chance of succeeding?

I realize that the backup difficulty class casts the scales with the caster level. This is for a low level module in which the DM has asked us to use the punctual purchase system of the PHB and ban the minmaxing, so:

Please assume that any given DC is between 12 (8 + 2 skill + 2 ability modifier) ​​and 14 (8 + 3 + 3).

Although I am interested in how this might change at higher levels, this is not the main focus of this question.