This.
If you're building a ship to explore the Guardian sites (much like the 'goid sites before them), one of the most important criteria is the ship's footprint.
Basically, the DBX or Dolphin are going to be much, much easier to land as a result of them having a narrow footprint.
You
can land a ship with a bigger footprint but it's much easier with the DBX or Dolphin.
Not sure how the space-bus stacks up against the DBX in other regards.
It has, IIRC, got the most slots of any small ship but it's also got puny hardpoints and, well, it's a space-bus.