During very low light big-objective (50mm+) binoculars will generally transmit more light. However, most are surprised to find that those same big-objective binos are not appreciably brighter in full daylight (our non-dialated pupils simply cannot absorb it all) and any aberrations or optical imperfections will also be magnified. So, only the finest quality optical designs really shine here. Fortunately, both the SLC and HT 56mm binos offer particularly spectacular views any time of day, but especially in low light.
Both the 8x56 SLC and 8x54 HT are still in production (both lines retired their 42mm designs). They both have AK prism designs (to maximize light transmission) and only the best coatings and glass offered by either company. Both have spectacular resolution/sharpness and pleasant views. However, they are very different products. I find the Zeiss the better handling of these two big binos, and if I were looking to use it as an everyday glass may get me to lean in that direction. To me, the SLC has slightly better colors and a larger “sweet spot.” I also like the focuser on the Zeiss a little better. Either is a fine choice.
The 8x42 SLC (better choice than a 10x42 in low light) is also an excellent choice for an all-around glass. Its low-light performance will be a smidge behind its 50+mm big brothers, and those bigger glasses due to using AK prisms will have a slightly better 3D effect. However, the 8x42 SLC handles leagues better. So the real tradeoff is better low-light performance of the 54/56 vs the still great views and much better handling of the 42mm. The full-daylight view of the 42mm is very close.