The minimum requirement for a single ADF is usually put at around 2.5 - 3 gallons, so a 2g IS cutting it a bit short, and you absolutley will not be able to keep more than one alone in a tank that size. Well planted is always good, mine definitely enjoy their greenery.
That said. . .
I don't know how to compare the two - they're really apples and oranges! Maybe Gizzy will be able to shed light on the bioload aspect of things. I DO know that they require very stable water parameters, and will do better on the softer side of water. Even if your 2g can handle the bioload, you have to consider the needs of the frog. They're active little guys, and really do like the extra space that a bigger tank brings them. I have my 2 in a 5g (which unfortunately for them is a hex - taller than wide), and am planning to upgrade them to a 10, just to give them more room to spread out.
I love my frogs - I enjoyed her when I only had one, and I'm finding them more entertaining now that I have a pair. I always see mine. They ARE nocturnal, however. Though they are less active during the day, mine are still very much around even during daylight hours. There is no doubt, however, that their activity picks up in the evening. I've found that when I feed them at around sunset (6pm-ish) they reward me with a ton of activity before I'm ready for bed. I don't know what you would consider entertaining enough to take up the space. . . they definitely are less active when the sun is high, though. (and I'm sure this varies from tank to tank and frog to frog). *I* find them very entertaining to watch at any time of day - but I can't tell you that you will, lol! It all depends on what you're interests are!
Hope this helps. . . but keep in mind that you ARE posting on the ADF thread - of course we're gonna say we adore our froggies!
ETA: AAAAAH! THERE you are, Giz! Beat me to it! I love that you're back. . . you're so much better at flat facts than I am *hugs*