Great Information Ken.
"Speed" isn't as big a deal to me and my Wife, but Adequate Power (to get up a hill, or move us along easily) is.
Which motor addresses that best.
I agree with what Ken wrote regarding the mid drive. From a practical standpoint they can get by on less power than a geared or direct drive rear hub due to the advantage of having all those available gears (assuming only there's a rider aboard that understands how and when to shift those gears). This is much like the current rage in automobiles. 15 years ago few cars/pickups had more than three speed transmissions. Then it went to four speeds, then five, and now 8 for pete's sake, all in an attempt to keep a grin on your face while using less power. Less power = less fuel = better fuel mileage, right? On a bike, using less power = better range.
So on the geared rear hubs, they generally have a single fixed 5:1 gear ratio. This means that all else being equal, when compared to a direct drive hub they have quite an advantage when it comes to accelerating from a standing start or when climbing hills. The issue with geared rear hubs (and mid drives) is getting rid of accumulated heat. They're not so good at that, so you don't see them with the big wattage ratings (like 1500+) available with direct drives. Also, because of the 5:1 gear ratio, they run out of breath at lower speeds than the direct drive (20-30mph depending on the motor).
On to the direct drives, the smaller ones are pretty gutless from a standing start or climbing anything but the slightest of hills, as they have no gears. Kinda like accelerating away from a light with a car/truck/motorcycle in top gear. Not so impressive performance. To make up for some of that, they use larger diameter (heavier) motors to take advantage of the extra torque available due to that larger diameter. AND, these direct drive motor rear hubs are very good at dissipating heat, so they can feed a LOT of wattage into them as the heat generated by that wattage is easily dissipated. My impression of a direct drive is simialr to a diesel or a turbine. You put your foot on the mat and wait for it, while monitoring your speed closely, because if you don't, you're very likely going to overshoot yor intended speed big time! They are so smooth and quiet, you don't notice how fast you're going!
So, though the geared rear hubs are good at accelerating and climbing, they aren't as good as a mid drive with somebody that's willing to optimize available power by staying in the correct gear riding them. BOTH of these geared systems are going to be out run by a direct drive at high speeds (over 25mph). The direct drive is just starting to get efficient at those speeds....
If we assume riding for pleasure only, and define our playing field as paved, with no speeds over about 20mph necessary or desired, the right bike will depend on how much performance you're happy with from an acceleration standpoint. I like to be able to squirt across a busy road post haste (hanging on tight), but the power to do that could scare some riders. So this is a personal call. My choice would be geared. Either the mid drive or a geared hub.
Then there's also hills that must be dealt with. At speeds below 20mph, my choice would be geared again, taking advantage of the gears to develop more available torque. The direct drive, even a big one like the 1500w I'm currently riding, can run out of steam on the longer steeper hills. The downside to the geared systems in the hills, as mentioned earlier, is heat buildup. While they can make the necessary torque required, they're very likely going to need a break before doing it again. -Al
