When my friend murk and I play, one on one, we usually turn off items. We prefer it that way. Sometimes after a few matches of nerve-wracking intensity, we'll loosen up by playing a Bob-omb Match (which is where we get the two of us, set Bob-ombs as the only item on high frequency, and play on Whispy Woods with two low-level Pichus as punching bags), which is basically just for fun. Sometimes we'll do items in our battles, but very seldom.
When we play with more people (we usually only play one on one when we're alone), it'll usually be with items. Of course, we're usually the last standing, each of us with five lives left while everyone else is dead. But we all have fun playing, and they even enjoy watching us fight each other. Just watching us is intense.
I like without items just as much as with. Using items certainly takes skill, and there's certainly techniques that can be used with them (I barely ever use them; even when they're available I'll just grab them and throw them at an opponent or off the side of the stage. That's why I like items like motion sensors and stuff, because I can use them immediately. One of the few items I'll hold and keep is a beam sword, and even then only occasionally), but the two modes of play are different in a lot of ways. I'm not going to make some definitive statement on what is "pro" or not, cuz I think the entire idea is ridiculous, but I personally feel more challenged and more engaged without items, on final destination. Items cause more chaos, so the game becomes less about fighting and more about keeping your wits about you and surviving. A different skill entirely.
When my friends do play with items, we usually turn off items like healing items, pokeballs, and a few other things. Murk often turns off star wands because I discovered that Fox's shield can't deflect them.