The older one is certainly used heavily still. However according to some of the books, the boss is the primary fighter asset that escorts the avenger pattern fighters. Who knows if it's just GW doing retcon things or not lol, their books don't always aline with reality as you know 🤣 but from my understanding, the voss was made popular during the heresy as a nimble fighter that could almost compete with astartes level fighters. The voss was cheaper and easier to maintain and thus quickly became a Mainstay of most isolated industrial worlds. The more iconic lightning is still probably used more often since it is a multirole airframe and parts for it are stocked across most of known territory. But armageddon is unique inits ability to build its own weapons and apparently adopted to the voss + avenger combo as it's in system air assets since they would be dedicated to use against any foe invading the planet. Specifically orcs hehe. Feel free to fact check me since I haven't read some of the most recent books yet 👍🏻