They all tried to match each other in terms of features. Frames made later in the 80s have more features: rack braze-ons, water bottle braze ons, dropout adjuster screws, lowrider braze ons, canti mounts, etc. Later bikes also have lighter tubing that is in some cases triple butted. For example, a Miyata 1000 at the end of production in the 80s is far superior to a Miyata 1000 made in the early 80s.

So, it depends not only on manufacturer but more importantly on year.