Get the one you like the most. They're all hax. Besides, you'll eventually get one that's more hax. But... since panda's disappearing I'd say get Panda. They continue to grow for a loooooong time, so even though you can only get one pet by choosing panda, it's not a bad investment. The others will be there to stay.
My first pet was the Silver Fox, which I got primarily for companionship.
Even though its growth is stunted at Age 5 and its inventory is mediocre, it backs up what I said above: they're all hax. Even the least hax is haxed out, lol.
In Ragnarok Online, I was once known as Athero, a noble Lord Knight whose only wish was that he swung his sword for a just cause.
TrueSilverFox and Mon_Ami roamed Caballa together in Trickster Online, searching its ruins of splendor.
Valeria, sworn only to her sword and herself, traverses Erinn in Mabinogi with her pet silver fox, Truesilver.
"Whoa, TrueSilverFox, girl! Anyone ever tell you you look like some sun-bronzed Greek Goddess these days?"