From Dragon of Desire:

At first glance, the best armor SEEMS to be the Quantum Suit. But it's horribly obsolete, doesn't have some QOL features of later mods, and is otherwise inferior. The Better Jetpacks 2 Mod has the Flux chestplate, but this version of Thermal Expansion doesn't have the rest of the suit. This makes me believe that the best option would be to get one of two mods; Draconic Evolution (you'd need to do a bit of recipie changes to give chaos crystals and dragon hearts and Draconium and etc for the higher tier, since we don't defeat the ender dragon or have access to the End) or you can go Modular Powersuits, which is an older mod but works quite well.