I personally like the footprint of the 120, but the 125 has more surface area. 9 square feet vs 8 square feet on the 120. The 125 also has a longer run for nonstop swimming. You can still do your palidarium since the height is the same.
If you are interested in adult frogs I will keep my eyes open. I just passed on several. I will be in you general area in July for a couple of days.