There are many variables, just a few of which are:
How long has the server been around? I play on both A and U, and I find that it is much easier to find earlier-era Goods on U than A for the obvious reason that more players on A are in the late-Era portion of the game.
How spread out, in terms of Eras, is your Guild? This is a sub-problem of the above. If you're a new(er) player in a Guild full of well-advanced players, while they might be the most helpful bunch, there's not much they can do if the earliest Good they produce is Colonial and you're in the Iron Age.
What type of player are you? Everyone seems to complain about limited space in the game. If you're going to be a PvP or GvG-er, space for those military buildings, and likely that of the GBs that give military boosts, has to come at the expense of Good-producing buildings (although this can be at least partially offset by the Goods you will Plunder from other players). If you're a Farmer, then you have to devote space to your Coin and Supply buildings and the GBs taht support that and keep your military up to date enough to at least try to deter would-be Plunderers. All of those force a trade-off with Goods buildings, so maybe you have room for only your current-Era ones.
For myself, I generally will keep Goods buildings for my current Era and the one below it. I feel that gives me at least a little bit of flexibility in trading or when I Negotiate for sectors and provinces. I also find it to provide a decent balance between efficient use of space and population and my playstyle on whatever given world. Your results may vary.