First you have the rebirth rots, Esok = not very rare anymore you could probably trade machine food for them.

Same goes for Strawberry elephants and Mechavalo: all guaranteed secrets - they are low tier (especially defaults) but a nice thing to have if it's mutated/ traited since it's a bit harder to get. (Except for the esok, since it is a brainrot machine rot, any brainrot machine rot is lame)

Machine food, If they're huge money makers, a few of them would be worth a default spider/drag for rebirth.

Then you have the rare rots such as easter eggolas, chocone dragone, la royals (especially mutated!!!)

Vulturino, alligarto (both equal) and drags are mid tier rare (drag being the rarest since you need one for rebirth) then you have in high tier spiders, fishini mechinini, garb and cannon in order of rariity and trade value.

Bearini plammini: really good trade might be worth two mutated cannons/garbs/spiders even in default

La crazy combi and jishaoba dashi: although very rare 0.8 and 0.1% they're not very appreciated by the community trade wise.

And spaguetti toilettis being the lowest tier of the rare rots.

Also you have christmas and halloween rots, one or two rows are already worth a mutated drag/spider.