Starting items tierlist:

General: (As a general rule, i do not check curse rooms while resetting so items like brim are not starts)
God tier: Knife, Ipecac
Tier A: Epic fetus, Dr Fetus, Tech X, 20/20.
Tier B: Crickets Head, Magic mush, Judas shadow, Lil Brimstone, Proptosis
Tier B-: Monstros lung, sac dagger, deaths touch, Crickets body
Tier C: Poly, Quad shot
Tier D (Not real starts, only check-curse-room or desesperation start items) Choco milk, The mind, Guillotine, Crystal Ball

Character-specific:

Eden: Not running anything that is not a tier A+ item or a B- item with something else (Like Mush+Pact in curse room). Synergies between items not listed there like tammy brim or isaacs heart blood rights are a start obviously. Checking b1/b2 treasure room with Isaacs heart or Blood rights (Looking for the other combo piece)
Blue Baby: No specific changes
Maggie: Judas shadow is tier A.
Samson: Scapular is a tier B start here. Also crickets body is not a start, and prop is tier B-.
Eve: Curse rooms are worth checking if i need to catch up.
Cain: Crickets body is not a start here due to range.
Judas: Not checking curse room with tier D items
Isaac: No specific changes
Lazarus: Check for telepill into i am error room with tier D items, check for tears up pill with mind.
Azazel: Unbalanced char boys, no specific changes.
The Lost: Sac dagger is not a start here.
Keeper: Quad shot, poly, crickets body and tier D items are not starts here.