I have access to a treadmill that has speed workouts and incline workouts. There are two types of each - intervals and ramps. In an interval, it alternates between a resting speed or resting incline and a working speed or working incline, with each interval being 1-2 minutes. In a ramp, the speed or incline starts low and increases to a maximum about half way through the workout and then starts to decrease. There's also a combination ramp that changes both speed and incline through the duration of the workout.
I'm guessing that there's no one best choice - there are benefits to intervals and benefits to ramps. I typically do two treadmill workouts a week - one focusing on speed and one focusing on inclines. I'll do other easy runs or long runs on a treadmill if the weather is bad (or it's winter) or I'm crunched for time.
I found some information about speed versus incline intervals and the merits of both, but it doesn't discuss speed and incline ramps where the whole workout is a build up followed by a decrease. Another article mentions "hill training" for use if outdoor areas tend to be flat (which is true for me), which sounds like incline ramp, but doesn't compare it to intervals. Another article talks about general benefits of incline training. Finally, there are many articles which suggest that you should have an incline of about 1% on a treadmill if you are training to run outdoors.
How can I decide if I should do an interval or a ramp? My instinct is that I should mix them up, but I'm not sure if I should favor one or the other.
Should I continue to separate speed and incline workouts or should I tend toward the ramp that increases both speed and incline?