I know I made my option known a bit flippantly, but I weighed my options as well. If I may speak for the "both" crowd a bit?
The 3DS offered a series I love, anywhere, anytime, on a system I already owned, and sooner than a console version. That's what we call a snap keep. It does however force me to concede a different control scheme; even the new 3DS, with its much hyped Nintendo Nipple C-stick has a starkly different feel from the GameCube controller, and the tiny screen makes precision more of a challenge.
The Wii U version by contrast not only limited me to locations where I could haul and hook up the console, but also forced me to not only make a sizable investment that I would be unable, with my titanic CRT, to utilize to its fullest. And, perhaps most criminally, it would force me to wait a month. But in exchange I would be granted usage of a fresh outlook on the series in familiar settings (and with familiar controls), and the opportunity to set up the kinds of side-by-side play that hooked me so deeply on Smash in the first place.
This isn't an argument itself, however; these are just the pros and coins that made it difficult to choose. My decision was solidified when I came into a source of side income that I could earmark safely for the Wii U console, and the knowledge that I would likely get other games for it as well (I'm looking at you, Zelda Wii U), making it not a one-title investment that would be difficult to justify.
I would say my position is unique, certainly, and hinged on things others may well not have. But I'll count my fortunes gladly, and scrub on both versions until they shine like diamonds.