I prefer hard luggage as it protects any electrics such as a hairdryer or straighteners from being crushed, particularly during loading and unloading at the airport. My case has hard outer coating, but the zips are expandable at the sides to give that little bit of flexibility!
When I was a road warrior, I liked the luggage with a solid frame and wheels, but soft ballistic nylon, especially the expandable variety. It was strong enough to protect anything, very light weight, and, without expansion, worked as a carry-on, and with expansion, could carry clothes for a week.
I used hard cases only when I needed to make sure a laptop computer or similar device survived being checked as baggage.
A true road warrior should buy them with a replacement guarantee and get new ones every 2-3 years.
For me, hard luggage is better than soft luggage especially if I have some electrical things inside. Besides that, it´s more durable than the soft ones and I could adjust the sides with zipper as it will expand and I can put some more things inside.
I'm going against the norm and saying soft. Whenever i travel, i usually carry my fragile electronics in my backpack and a military style dufflebag slung over my shoulder. It's easier to compress more into it and is easier to push into tight spaces. Not to mention if i take it on a smaller aircraft i can get it into the little overhead compartments or under the seat, unlike hardcases.