Not to go off-topic too much (uh, epic fail already, haha), but I'm a big goldfish fan, if you can't tell. :) Anyway, the orandas, especially the veiltails, can be quite delicate - prone to damage and infections of the hood, prone to fin damage and therefore rot, very prone to swimbladder disorders with any kind of infection or just "because," constipation, etc. I don't even have to get into the problems of telescopes, celestials, bubble-eyes, and lionheads (celestials and lionheads don't have dorsal fins, poor things!) Of course regular goldfish are much hardier, but Comets do have a greater chance of fin damage, like long-finned bettas. And if you've seen goldfish spawn, you'll know I mean about fin damage. :p
Anyway, I thought bettas were hardier, myself, until starting to haunt betta groups recently. Now I have a much better appreciation for how much more care they need than some of the more hardy tropicals! I have some loaches in their early teens, and I've got to tell you, despite their reputation, I can hardly think of a way to kill them except remove them from water altogether, lol.
Oh, and I had a betta sorority a few years ago, and those little buggers are quick! I did find them pretty, but they weren't particularly peaceful and relaxing like I find the males. If I get a Plakat or wild-type male, though, we'll see if it's the same. o.o