Landers: heavy and efficient vs. lightweight

[WarWyvern]

I'm planning on making a series of interplanetary missions to test designs for a possible grand tour of the Kerbol system and found myself with a slight dilemma: my proposed transfer vehicle can't mount a small lander inline, so I'll need to bring two. That's fine, except the nuclear landers that I've always built (based off of those frequently employed by Scott Manley in his videos) weigh in at a mighty 17 tons, whereas a smaller design I've been playing around with is a much more reasonable 7.28 tons, but lacks high-efficiency nukes in favor of the Rockomax 24-77 radial engines. So, I decided to test the two with a Mun landing exercise.

The mission was to use a transfer vehicle to tug the landers to low munar orbit (about 15 km), pick a landmark and deploy one lander over it. Once the first lander touched down, the second would be deployed over the same landmark on the next orbit and touch down in the same general location as the first. Fuel would be compared between the two before they lift off into an orbit matching that of the transfer vehicle, where fuel is compared again. Note that I only rendezvoused with the orbiter after the experiment was concluded, in an effort to eliminate what variables I could.

What I found was that the larger craft used 128 units of liquid fuel (36%) for its landing, while the smaller craft used 152 (42%) with a bit of inefficient pogoing due to an unskilled pilot. However, the larger lander achieved orbit consuming 112 (totaling 67%) fuel and the smaller a mere 94 (68%). Since they both used the "tuna can" with 360 units of liquid fuel and neither emptied it, that is what I used to compare fuel percentages, even though the larger lander had a pair of side tanks to mount the engines onto (90 liquid fuel each). These results make the difference in fuel efficiency of the engines seem negligible, but the lighter lander design would have an advantage in not driving up the mass of its carrier, making it easier to fly.

Because I checked and didn't see any topics like this and have found myself falling into a pattern of building the same lander design over and over, I thought I'd submit this experiment to the community to see what you all think and maybe help out those who haven't experimented with different landers (also to double-check my math). Is it a better choice to pick raw fuel efficiency over a lighter design? If so, how do you offset the additional mass that more robust vehicle brings?

Thanks for reading.

[UmbralRaptor]

There are design ranges where craft using lighter low Isp engines outperform heavier high Isp ones. That said, I would expect anything using the Mk2 lander can and a rockomaxx x32-800 to push you outside of that.