Reliability and build are all relative to the brand not the size. That said a 30’ Mh with a longer wheelbase will ride much smoother than the wheelbase on anything 27’. The smaller the RV the rougher the ride (in general). A longer wheelbase dictates a smoother ride. Heavier can also be a benefit with respect to ride but perhaps not MPG. In terms of MPG the AXIS will be the winner here with probably double digits. The rest on the F53 chassis will get about 8-9 mpg. But the AXIS is a first year model. Lots of bugs to be worked out of that one yet. I would wait for at least year 2 to get some refinements. Some other things about the axis is that it’s on the F450 chassis. Same as a class C. So it will ride much rougher than the F53 chassis that standard class A’s are on. I also didn’t like the shower in the AXIS. It’s small , the curtain, and runs a hose from the faucet. Haven’t seen that since pop ups. If you are going to be in it weeks at a time, you will want space and things that can lend itself to daily living. For not much more money you would be surprised how much more comfortable you would be and how much more you get out of an RV that’s 3 feet longer. Just saying. Our ACE 29.1 gets a bit cramped even at 30’. The 29.2 is much better. Same length but the full wall slide really opens things up. Point being we usually only take week long trips and I could not imagine going smaller than 30’. That’s my opinion. Also if you plan on taking a car or gear you need to look close at real carrying and towing capacity. Some small RVs will leave you almost nothing in terms of CCC. Nothing worse than spending all that money to be miserable on a few trips and wish you’d gotten the bigger one for almost the same money. Cuz once you own it you’d take a bath trying to trade on what you should have bought in the first place. Take your time, spend some time in an RV like you live in it. Might be a good idea to rent a 27’ to get a feel of what it would be like. Then walk through the 30.
BTW - 30' is not big. Small by class A standards. 40-45' is big