I liked my 3DS and XL, but I could rarely conjure up the will to play them.
The Switch is such a great piece of hardware. Games that I loved, but didn't feel like completing on other systems (e.g. Shovel Knight on 3DS) I just can't stop playing on the Switch. I haven't been this excited to just play games on a system since... ever, I think. Maybe since the DS. I really feel like the Switch has revitalized my interest in gaming.
A huge part of why it was revitalized is because of how versatile the Switch is. I played Zelda on the TV with the Pro Controller, then I would undock and remove the Joy-Cons, and suddenly it was a 7" tablet that I could inconspicuously carry on the train and play Voez with the touch screen. It was insane to think that the same system was playing both games. Meanwhile, with the 3DS I was often wishing for a way to play its games on TV. (The Switch's screen being so big doesn't give me this feeling as much.)
So basically, I don't think I can go back, lol. It's a shame, because there are so many games on 3DS that I love, but don't think I'll play again... When 3DS emulation improves, I'll definitely replay some games on my TV (namely the Kirby games), but beyond that, I think my 3DS will mostly be collecting dust.