Hey Terry, I’m think I’m going to say that, though the coker ride would be better for cardio, the muni ride would probably take the coker ride in terms of brute short-term power output training.
They’re really two completely different kinds of training. When I’m on my bike I’ll easily go 90-100 miles, but those 90-100 miles are in a gear where I actually have some good resistance, allowing me to put out 180-220 watts for an extended period of time, which is where the workout is. My heart rate may only be 120-140 the whole time, but it’s definitely raised, and I’m definitely hammering pretty hard to keep speed up. I would say that a long bike ride like that is definitely more similar to the coker ride than the muni ride, but on the coker, you’re stuck in a 36-inch “gear”, probably limited to 50-70 watts of average wheel-to-ground power output, plus maybe 20-30% extra effort in order to keep your balance. On the bike you can hang in the 30s-40s for climbing (high cadence, power-spin!), 80s for flat speed, and even 100-140 if you’re feeling like a god for the moment, allowing you to actually crank out more physical work, in the strictest sense, force-distance units at your pedals. On the coker, without getting your cadence through the roof, it’s impossible to work yourself out! That said, I think the coker ride is mostly useless unless you either put in long, long distance or get a Schlumpf hub and frame and ride in 54" mode to force yourself put out more power.
Riding a unicycle cruelly limits you in how hard you can work yourself at reasonable cadences. Go geared (which, even then, may not be enough) or climb hills. You’ll need to find the right hill for optimum effect because you can’t shift. In a 36" gear, probably an 8-10-percent grade, six or so if your strength isn’t quite there yet; that’s what you’d want to do if you’re going to train road. If you do do that… climb hills all the time, etc, you’ll have legs of steel and will be able to power through just about anything at really high output for a long time. Which brings me to the muni ride…
My problem with the muni ride is that it’s only 35 minutes long. Granted, it may be an (exceptionally!) intense 35 minutes, but as far as a “workout” goes, it should be far longer, probably at least into the 1-2 hour range. The muni ride will get your heart rate up into the sky, but it’s because you’re doing obstacles, rough stuff, pounding all over the place, standing up, etc. The muni ride will really help your ability to maintain fast, intense stuff for minutes at a time (like, if you’re going to max yourself out for three to five minutes at a time), but I wouldn’t say it would increase your ability to simply put out RAW POWER at any time you need it. It’s great general conditioning, but you’re not going to become a mad sprinter or hill climber doing it. Thing is… if you DO become a great sprinter or mad hill climber, what the muni riding will do for you is to allow you to get your heart rate down more quickly after powering, and it will allow you to keep up an almost-sprint level of output for much longer.
You actual ability to crank out power at any given time, though, like, how hard you can push when you’re fresh, and what kind of foot-on-pedal force from your leg relates to what kind of perceived effort in your brain, will come from high-gear/uphill coker riding (or, if you really want a quantifiably intense road-based workout, a road bike where you can always choose a hard/optimal gear for good resistance at high cadence). Unless you’re climbing, on a coker, you can have all the cadence you want, but you’re not going to get the ability to acutally push hard at that cadence, because a 36" wheel (and perhaps even a 54") just isn’t big enough. The 54 would definitely be big enough to get you a good long-distance flat-ground aerobic workout though, if cadence stays up.
I’m sorry I’m so long winded… I’ve thought about this a lot myself (and actually experimented with it and spoken with a bunch of people about it). But my basic point is… think about what kind of absolute foot-to-pedal wattage feels like in terms of the way you perceive how “hard you’re pushing”… that’s going to be amped up by doing hills on your coker. Now think about, when you open your throttle and start powering for a given amount of time, how long it takes you to feel the burn in your lungs, heart, head, (and perhaps legs, but not always) and at what level of fatigue you let yourself crack; the muni riding will postpone that burn and allow you to put up with more of it before your body’s incessant, most likely painful, complaining forces your mind to give it a rest.
If you can, climb hills in a tough (but aerobically friendly) gear on your road bike (if you have one) and keep your RPM up with a heavy gear. Do that a lot, and that’d be even better than the coker riding for upping your ability to just put out power.
If you’re going to rely on muni riding for core strength and cardio (which is what I think it’s best for, contrary to muscle, as many here have said… unless there is substantial climbing) then I’d make sure the muni ride lasts at least an hour, preferably an hour and a half or two, and keep your heart rate above 130 the whole time with a break in the middle… maybe 5 or 10 minutes at 130 and 5 or 10 minutes at 160-170 if the terrain will allow you to manage getting your heart rate that high (flat terrain, unless you’re really spinning FAST, won’t and shouldn’t get your heart rate to 170). That’s really good core and cardio, and the punishment will allow you to take more in the future.
If you’re wanting to increase how much power output you get out a given perceived effort, ride your coker on as many hills as you can find, or grab a road bike and shove it in a good gear (probably better than the coker). The best RPMs to do that in are in the 80-100 range, so just take as hard a gear as you can possibly do without letting your cadence drop below 80 or so. Likewise, if you’re on a coker, take as hard a hill as you can without letting your cadence drop. And when I say hill, I mean at least a half mile or so, though one and a half to three would be better. Going for a flat coker ride with three or four 200-yard hills isn’t going to get you very far. 
If your cadence goes too low during a climb, shift down! And if you’re already in first gear and your cadence drops uncontrollably, go home! And if you’re on your coker and your cadence hits rock bottom, suck it up or find a shallower grade. (But always make sure you’re on a steep enough hill to have to crank the pedals to keep your cadence going… it shouldn’t feel like it’s going by itself.) That will get your legs beefed up in a hurry, so that you’ll get a bunch of power for what doesn’t feel like much effort. Then the muni riding can make it so you can use that power-power-power repeatedly without bonking halfway through your ride.
Okay, I’m done now, I promise.
All that said, I’d alternate the ride. Longer muni ride, steeper or geared up coker ride. They both have their place, they both will help you out if you do them right, and, they’re both probably buttloads of fun!
Still i can’t help thinking that the 
), and I would think every now and then dismounting and mounting again as part of the training.