RPM or Resistance on Recumbent?

What do most of you watch?

I used to do interval and alternate resistance.

Seems like the HIIT folks say to go on one resistance and drive RPM up and down?

What is a good high end RPM?  120 125?

Any thoughts out there?

I ride a regular bicycle so I don't know how this will compare to what you are doing but typically you want to keep your cadence (RPMs or PPMs) between 80 - 100.  90 has long been considered ideal but the trend lately is toward the higher cadences.  Then when you do your intervals you will either increase the resistance while maintainingyour cadence to build strength and power or increase your cadence while maintaining resistance to develop your pedalling fluidity and cardio endurance.  

For the cadence drill you increase pedal speed as fast as you can but when you become ragged you back off so your are still fluid and hold that for 30  seconds or so.  The goal over time is to be able to pedal fluidly at the higher cadences of 130, 140, or even higher. The typical cyclist will do both of these drills at some point during the week.

For resistance drills you keep the cadence steady and up the resistance to the point where you can barley hold you desired cadence for 30 seconds.  Ideally the amount of resistance you are using will increase over time.

As an aside, the Tabata Protocol which many believe to be the most effective way to build power and endurance was original designed for speed skaters but was done on stationary bicycles.  The athletes maintained a constant cadence of 90 with the resistance begin increased during the on phase of the interval. If the cadence dropped below 80 before the end of the interval the the resistance was reduced a bit.The basic TP is a 5 minute warm-up with a 4 minute interval phase consisting of 20 seconds increased resistance followed by 10 seconds of recovery repeated 8 times.  Then you warm down for 5 minutes.  The entire protocol is over in 14 minutes.

So I guess my answer would be to do both, some intervals where the resistance level allows you to spin up to 125, 130 or even higher and to do some where the resistance will barley allow you to hold 90 through the duration of the interval.

I don't recommend doing intervals on consecutive days.