It depends. So if you want a universal shade, Nuln Oil is probably the best, as it’s neutral. But it can leave some colours looking very oily, and on lighter colours can look way too stark, so you’ll want to water it down for lighter colours, or invest in some other shades down the line.
Another good universal one could be Agrax Earthshade. It’s almost as dark as Nuln but is browner, so it is great for any warm colours you have, or for making other things look a little war torn/weathered. Again, you’ll want to water it down for any lighter colours since it’s so dark.
The others are a little more specific, tending to be for lighter colours or colder tones, etc. so they’d be good to branch into the more you get into painting. But those 2 mentioned above,
imo, are the best for starting out as universal shades.
I hope this helps, and welcome to the painting hobby!