Agreed, with equipment I go in the following order:

Ring > Bracelet > Earring > Necklace

The reason is simple... more stats. Atk items don't get as much out of upgrading but they start so high that they are too good to ignore. I will make exceptions for girls with low defence tho and go Bracelet first just to keep them alive longer.

Oh and before I forget... ignore normal Items, just stock them till you get Mid Grade items to upgrade and IMHO don't bother upgrading anything less then +8, ideally stick to all +10 but realistically +8 and +9 are still worth the effort.