I would def go with an 18x18x24. The other is so very small. I have both. My son got me the 12x12x18 for Christmas with a light and a GC for a frog. That's what started me on this crazy journey. Once I started researching I quickly realized that the tank was just too small, especially as I wanted to get two frogs (WTFs are social... or at least tolerant of each other). I'm super happy with my decision. I don't have a water feature but I do have a large soaking pool for them. You can look at my albums if you'd like to see what I mean.