While I am relatively new to the hobby, I would recommend larger. This is based on my experience with a Bubble Tip Anemone (BTA).
My tank is approximately 125 L (which I believe is about 33 US Gal). I successfully kept the
BTA in that tank for about 9 months, but unfortunately I didn't have a chiller and my tank overheated at the start of summer.
The reason I recommend larger is this: When we bought it, the
BTA was about 3 or 4 inches across. Within 3 weeks in my tank it had grown to over 12 inches in diameter and cast a shadow over almost half my tank. This wasn't too much of a problem in my tank, but if the tank were much smaller, it would have been as I would have had no space for coral.
Incidentally, the
BTA is still alive now, but it has
bleached (refer to my earlier post in the Invert section).
