I have been using my good old Type-6 for a big part of my work, still, planetary visits included.
I actually really love driving around in the SRV (except sometimes on low-G planets), so I have done it in most of the ships I have owned. The Type-6 seems, to me, to be the best compromise of maneuverability, speed, weapon placement, and cargo capacity. Maneuverability is not impressive, but it is enough to position your thrusters if you really get yourself into trouble, and a single boost tends to get you out of it. The weapons are underneath, which give you a good line to attacking skimmers (obviously, I am not thinking settlement assault for this; for that, get something with more muscle, maybe a Keelback if the T6 is still your thing). You can easily get 100 tons in a Type-6 while still having your SRV bay and a shield generator, too.
I was planning on messing around with an exploration build that could do SRV, and from an internal compartment standpoint, the Imperial Courier and Viper MkIV are looking really good. Pretty much anything with at least six internal compartments should suffice, but you really only need four for a dedicated planet-bound ship (I am even considering an Imperial Eagle or Hauler just to do planetary stuff). Having at least two medium hardpoints for missiles and one or two other hardpoints seems like a good place to start for settlement assault.
Smaller ships are usually easier to work with for planetary stuff because it is easier to find a landing place on rough terrain. It can save you lots of time when you can land right next to that crashed ship instead of 500 meters away. Picked up an Asp Scout for comparison (and because it is super fun to fly), and the smaller footprint I have in the T6 really can make a difference. Anything Asp or smaller, maybe a couple things bigger, can even land between the two buildings in those kinds of points of interest.