Ok, yes, I know. I know all the reasons why the Chieftain is a better ship. But to be fair, I'm the guy who wrote this and said the Dolphin is the best exploration ship in the game, so I'm a bit obtuse when it comes to ship choices. So please, hear me out.
First, here is my current build. (Still working on lightweight life support, but the rest is all done.) My goal with this build was to make a "combat explorer" type ship. Something that can handle any PvE combat the game can throw at it and still jump a respectable distance. To that end, note that the current distance is actually 37.65ly due to the pre-engineered FSD that Coriolis still won't let me equip (and also the extra 15t of life support I haven't lightweighted yet, so probably ~39ly once finished.)
"But that's horrible jump range!" I hear you say. Actually, it's perfect. If anything it's about 3ly too much. The minimum jump range you need to reach Beagle Point without FSD injections is 33.40ly. Every ounce of range beyond that means you will be skipping over valuable things on the way. That's not exploration. That's a taxi, and I don't fly taxis. Especially not into combat.
Range aside, this ship has another feature that makes it a stand-out explorer, one that it shares with the Anaconda, Dolphin, Krait, and Python. It has a fuel scoop (or rather, a slot for one) that is a size larger than the FSD. This is the secret sauce to any good exploration ship, and why the DBX is secretly the most overrated exploration ship in the game (yes, even though I put it on my old list - I still love its aesthetics and weapons package.) This allows you to deep scoop a full tank while you're going around the star at full speed and turns fuel scooping into a passive activity rather than a boring chore you have to focus on, suffer through, and sometimes overheat from. This is also why the Challenger beats the Chieftain as a "combat explorer" - the Chief only has a single size 6 slot. This forces you to choose between a good scoop and a good shield. The Challenger doesn't have to make that choice.
"Okay, but why not just use a Krait or Python?" A good question with an answer that didn't make sense 2 years ago, but does now. The answer is because of Odyssey. With the launch of Odyssey, combat is no longer solely about space based warfare, and ground combat is now an integral part of the game. (Not going to discuss how stupid the thermal/kinetic weapon swap dance is right now. I said it's integral, I didn't day it was very well executed by FDev.) To make the most of this, you need something you've probably never bothered to touch before: Dumbfire Missiles. These enable you to clear a LZ in a way that literally no other ship-based weapon can, easily wiping out half or more of the opposition before you ever set a single boot on the ground. They are invaluable.
And they also eat up a weapon hardpoint for something that's very subpar in ship-to-ship combat. This is where the Challenger edges out the Krait and Pyton. With no less than 7 hardpoints, including three that are size 1 and thus largely worthless for space combat, the Challenger maintains space DPS on par with a Krait or Python but still has space left over for a pair (or trio, if you want) of dumbfire missile launchers. Importantly, they are also spaced perfectly to give you a good balance of overlap and coverage against ground targets, wiping out anything near the impact point in a single volley. Surprisingly, they're also actually not that bad in space combat, as long as your target is within 500m and roughly pancake shaped (they are VERY effective against NPC Kraits.)
If I had to name a downside for the Challenger, it would be the lack of a size 2 cargo bay and a 1D repair limpet controller. Without this, any hull damage you take in deep space cannot be repaired. Thus, I would not recommend this ship for long haul exploration, regardless of build. But then, there's not really anything to shoot at halfway to Beagle Point anyway, so as a "combat explorer" you should never be in a position where this ship is that far out in the black anyway. This build is instead meant as a short range explorer and combat vessel in one, capable of going on short excursions ~2,000ly from the bubble and shooting whatever you find there, then returning home. Of course, you could probably find a few friendly fleet carriers along the way to BP so you probably COULD actually make that trip in this ship, it's just not ideal.
That said, I'm going to try it next week. I'll let yall know. In the mean time, I can attest that as a "combat explorer" the Challenger is an absolutely fantastic vessel that is criminally underrated.