For a more detailed introduction to this guide please read the holy bis guide for the 10-19 bracket. I go into more depth there into stuff like what race you should choose and how to navigate these guides. So, without further ado, the best in slot gear for 20-29 Holy paladins for PvP and PvE in Classic WoW.
Headpiece
Neck
Shoulder
Back
Chest
Wrist
Hands
Waist
Legs
Feet
Ring Slot 1
Ring Slot 2
Main Hand
Shield
Off Hand
Dressing Room
So if your focus is Player versus Player and if we choose from the items above the most useful in PvP (those that give stamina, intellect, armor, healing) then your toon should look like this: Holy Paladin BiS 50-59 PvP.
If you’re PvE orientated then with my chosen recommended best items you would look like this: Holy Paladin BiS 50-59 PvE.
In my Classic journey, I built my Holy gear as a mishmash of both worlds centered around an aesthetic I enjoy looking at: Holy Paladin 50-59 BiS Alternative Design.