I prefer using fire against fast fallers and ice against floaties.
With fire, I can do things like dtilt into usmash or boost ball into usmash. I just feel like it's easier to catch them into usmash. Plus you can follow up afterwards with fair or uair. Or screw attack if you want to be that guy. Fire fair still combos floaties okay, but it's nothing your uair couldn't cover.
With ice, your upsmash can secure KOs off the top, which most floaties are susceptible to. boost ball or jabs can lead into it at high percents. Ice fair won't really combo but you might be able to get a dropzone fair off a platform fflc dash, fh fair. It's kinda like a slower nair with greater range. Real bad to use while rising, feels good when fflc'd. Dtilt doesn't do much on confirm, but I like attempting the cross-up with boost ball afterwards. Ice fsmash is nice after a dthrow at 0% because you'll get that second hit for a sweet 20% plus a follow up with anything you want - like jab dsmash or another dash grab. Ice homing missiles are good for pestering people with slow recoveries, like opposing bomb jumping samus, bomb jumping links, ness if recovering from a bad spot.
General consensus is that fire is better for combos and killing off the side. Ice for keep away and killing off the top. Sorry if my explanation isn't very good, I'm really tired right now.
