Finding a "solid" X-Ray resource pack for Minecraft 1.12.2 usually comes down to visibility and ease of use. Since 1.12.2 is a classic version for modpacks and anarchy servers, most packs are well-optimised. Top Recommendations Ultimate X-Ray (by PinkuR_):
This mod allows you to toggle X-Ray with a keybind (usually G or X ) and lets you select exactly which blocks you want to see.
For the solo builder or the modded player who has mined for 10,000 diamonds already, it is a time-saver. It cuts hours of strip mining into minutes of targeted excavation.
Designed specifically for modpacks like All the Mods 3 or FTB Revelation .
On multiplayer servers, the use of X-ray packs can be frowned upon or even banned. Servers often have rules against using such packs to maintain a fair and fun environment for all players.