HIIT vs steady pace

I do not use a treadmill but I would definitely say I prefer HIIT for a variety of reasons. Mostly because changing it up keeps me motivated, each interval is a new start to count down and push then slightly recover so I can push myself again. I also prefer the adrenaline rush that goes along with the high intensity that I simply don't get from a steady medium pace. I know there are studies done that prove higher caloric burn and all too, but I guess I'm more in it for the rush Pretty much the only time I'll purposely do a steady pace is on recovery day.

I like both. HIIT seems to help me burn fat. For HIIT on a treadmill I raise the incline to 10 and then run at a fast pace for 30 seconds and then walk for 30 seconds. I go back and forth doing this for 10 minutes with a 5 min warm up and cool down.

There's no "either/or" or "better/worse". A balanced fitness program--whether training for competition or for weight loss--consists of a variety of workouts.

Couldn't agree more.

Research shows HIIT burns more fat, and steady state can actually stall your weight loss after the fist few weeks. I do some steady state because I am planning a long bike trip, and want to build endurance for that trip. However if I was just working for fitness or fat burn, I would do only HIIT. I use a pyramid system with equal sprint and rest periods. 15 sec sprint 15 sec recovery, 30 sec, 45 sec, 1 min, 1 min, 45 sec, 30 sec and 15 sec. I also use the tabata plan 20 sec sprint 10 sec recovery. I do most my intervals on a spin bike, but I sometimes do the tabata with light weights, and weight lifting moves like burpees , or push presses.

Looking for opinions as to which is better: high intensity interval training on the treadmill or running for a long time at a steady pace.

Depends what you're trying to achieve, although there is a lot of BroScience around, as upthread. HIIT is magic and works for weeks and weeks after a 15 minute session

From the perspective of a runner I do, at the moment, five runs per week with a combination of:

Steady state at recovery pace of 6 minutes per km - 15 km once per week
Steady state at recovery pace - 5-10 km once per week
Tempo run 5 minutes recovery pace, 25-40 minutes of 4 minutes per km race pace
Interval run - 10-15 min recovery pace warm up followed by either 20 second/ 60 second, 400 metre/ 400 metre or 1km/ 3 minute intervals of maximal effort/ recovery pace followed by another 10-15min recovery
Interval run as above

Steady state builds endurance
Tempo and intervals push the capacity of the CV system, optimising conversion

I'd liken it to steady state filling the tank, tempo and intervals making sure that it's high octane. One without the others are a waste of time.