The Luna HD is one of the most popular texture packs around for Minecraft for a number of reasons. First is it is readily-available and ready to use, next is it is continually updated, support for multiple Minecraft versions and the amount of visual improvements it brings.
Luna HD contains realistic 3D models, better lighting, and more detailed shadows and reflections without altering the overall gameplay. Objects are now much easier to differentiate and tell apart due to the improved physics and visuals without the need to look at a block closely. This texture pack also supports and benefits from RTX graphics so you can expect a definitely better visual update in case you have an RTX Graphics Processor in use.