How do the controls on 3DS compare to console? I've never played it on my own time so I always just ended up button smashing with friends. I'm seriously considering getting the 3DS version just so I don't embarrass myself in the future.
The big difference, in my opinion, is the 3DS control stick. It's very different from that of a GC, Classic Controller or a Nunchuck. Or even an N64 one. It took me some time getting used to it, but now I rarely do a forward B when I intend to do up B. Aside from that, I did have the same problem as Sudgy (attacking instead of jumping) but that was very easy to get used to.
Did they flip the buttons for attacking and jumping?
3DS button layout is different from the typical Smash bros. (Gamecube controller) layout. Same named button does the same things, but they aren't quite in the same place. I had issues with this too when I played the demo on my friend's 3DS
It's interesting that so many people are having trouble with this; I didn't even think about it and was automatically pressing the right buttons for jumping/attacking. Maybe it's a difference between people who are used to Y-jumping on the GC controller and people who are used to X? (I usually used X in Brawl/Melee.)
What I found disorienting was L to grab; I'm used to using R to shield and Z to grab on the GC controller, so I want that finger to do both. I set Y to grab instead (since I can't have R grab and shield), which I like better than L, though I'm probably in the minority on that.
Is there a way to change the input?
Yeah, controls are customizable like in Brawl. It feels like there's less flexibility though, probably because there are fewer buttons/sticks on the 3DS than the GC controller (well, I guess just one fewer button and one fewer stick, but the absence of the C-stick is a big difference I think).