Vendor Recipe Q? - 5 Rare Items of Same

Vendoring a full set gives you 1 chaos. Getting the rings/amulet/belt is most difficult, so we can ignore the rest.
That means each ring has a value of 1/4 chaos. 5 rings -> 1.25 pure chaos
Vendoring 5 rings -> 1 applied chaos + 1 ring

This means the value per ring is theoretically equal.
However, vendoring a full set will give you the actual chaos orb which can be used on anything, but you pay a little more, because the rest of the set would give you some shards.
If you want to use a chaos on a ring anyways, you can also vendor 5 rings (but check the ilvl). This method also requires less space in the stash.