Height-wise, both look good and I think you will be happy either way. For the 2nd pic (maybe I getting the wrong impression from the pic angle), the only thing I would caution is the right-side underlying rock structure seems very "vertical" (in that not much extends out past the upper shelf rock). If you have something growing out horizontally on top then it may render much of the space underneath less usable than you would prefer.
If you haven't already considered it, you might look into using 3/8" acrylic rods (cheap on Amazon) and epoxy to fine-tune your rock height and/or help reduce the need of underlying base/support rock. I used rods to elevate my rock off the floor to help keep detritus from collecting. To a lesser extent, you can also use one or more of those square frag plugs to elevate things from the bottom where needed.
You don't have to do it now but, as you add frags, you could mount the frags to small scraps of loose rock/rubble and then glue that rock to the shelf. It will give encrusting corals more service area to establish their base without fighting with neighboring frags.
Well I finally took the plunge and epoxied the rocks in their final resting position. The pictures were hard to focus due to all the dust floating around (I put more substrate in too). I think it looks pretty darn good, and I feel like I kept things low enough that I have opportunity to let the corals grow.
(above) - Front side of tank. The middle Tonga shelf is about 50% high, and the right Tonga shelf is about 1/3 of the way up. My bubble still hasn't recovered from a phosphate spike a few months ago, and my gold torch normally looks way better than this, but he is upset with all the moving around I did today.
(Above) - Back side of tank. The middle tonga shelf is very wide, There is only about 2 inches between the glass and the shelf on either side, so there is plenty of room for some fantastic corals!