go with the bigger. more viewing area, more volume, more goodies. 8)
i wouldn't worry too much on the light penetration. not so much that it isn't true but there's nothing wrong with having various degrees of light intensity on the reef.
otoh, the dealbreaker for that would be if you for some reason MUST have some type of light intensive livestock that HAS to stay on the sandbed, e.g. maxima or derasa clam, elegance, etc.. otherwise, just keep medium to low light livestock there.
as for the depth reach-wise, either use dowel rods, a gripper of some kind, or just get wet!

i use stainless hemostats to handle most of my livestock anyways, even if they're just 6" below the waterline. the 24" hemostats should just about cover a 30" depth (taking into account the height of the sand and just getting a few inches into the tank).
but going bigger for your
display tank is always a good idea ime. for niche stuff, office, nanos, species, etc.
then it's whatever fits in the spot imo.