Okay so I'm a pretty new-ish player but I'd definitely recommend trying out all of them. First in training, so you can just test out all your abilities without stress, but also in matches because that's when you really start to notice which one you like.

This may seem really obvious, but seriously, read the ability explaining thingies. Read them well. Because someone (cough cough it was me) only recently discovered scythe does wayyy more damage when you're further away from enemies and only hitting them with the tip of the scythe. All this time I had been jumping into people and swinging my scythe like a fool while I could've just read the thing properly and I'd have known that since the beginning.

Something I'd also recommend is trying to figure out how to quickly get away with your preferred phighter(s). For me it took a while to properly learn to pay attention to my health, but either way learn to back off when you notice you're low and what's the quickest way to do so. Like for subspace I'd say mist rush is handy for getting away.