I've only used the shield-line, but I've put some thought into how to use each of them. Each one can be fairly situational.
The Gunrig is probably the most versatile and it can be really good, either put Darkstrider or a commander on it, and it would work really well verses MC's or Tanks. It can also still do stuff for less points, if you don't use one of the HQ choices to fire the Railgun, plus it has the re-roll 1's for everyone on it.
Maybe its just that the meta at my local store doesn't have an abundance of ignores cover, but I really like the shield line, especially with Sniper drones (BS5 Re-rolling 1's with 4+ armor and 3+ cover
). It would be all about how you use it, fire warriors without a fireblade or kroot without sniper rounds, probably wouldn't get too much out of it. But Pathfinders and Sniper Drones, get mobility while counting as stationary, re-roll 1's and the tidewall field. So it tends to be less versatile than the Gunrig.
The drone-port offers "free" drones, like our vehicles and it has the same re-roll as the others. I would take the other ones before the drone-port unless I wanted more drones of a certain type or a mobile cover save for a unit that won't draw as much fire as the gunrig.
I don't think I would use the Rampart unless it was in a very large game (>3000 points), maybe not even then. All the sections have to stay near each other and it would take up quite a bit of space so it would be hard to move.