The hitchhikers and biodiversity on live rock used to be an exciting part of the hobby. Most places seem to be switching to dry or painted synthetic stuff for sustainability or responsible reefing
. Any rock will eventually house nitrifying bacteria and be "live", but true live rock, uncured, will add all kinds of life to your tank. It's true that some live rock might unwanted pests such as red planaria, gorilla crabs, possiblly aptasia, and bristle worms (which i actually like). It's also true that true live rock, fresh from the ocean, will contain more sponge, types of coraline, and even different bacterial strains.
There's ups and downs with any rock choice.
1) I choose to use fresh from the ocean live rock and "cure" it in a garbage can until there is no ammonia or nitrite since die off will occur through shipping. This is the most expensive method, difficult to locate a good source, but I like the life on the rock.
2) My second choice would be live rock from a pristinely maintained reef that someone might be selling, but this can take some time to find in the sale forums.
3) 3rd choice some kind of clean dry rock and cycle in the tank. Downside is lack of biodiversity, and it takes more time to look natural, but still a good choice.
4) lfs store bought rock varies. In a maintained system it's usually ready to go. You probably won't even cycle, but some LFS's just throw their rock in a giant vat ad let it sit. This is the worst choice that you can make. Rock can be an absolute phosphate bomb. It could take months to clear the hair algae which will constantly regrow from the internal po4 source. Avoid poorly maintained rock at all costs.
Hope this helps, good luck!