My opinion - First, to qualify my thoughts, it should be understood I ride for pleasure only, with no interest in commuting. Second, I have no interest in speeds over 20 - though the bike is (as it is currently set up) capable of sprinting nearly twice that with the 1500w direct drive hub. Most of my riding is in the range of 8-15mph. I should also mention I'm a big guy (6'2"/315lbs).
I liked the idea of direct drive on paper (with few moving parts and no gear whine), but from a more practical perspective, they are hurting in the bigger hills. Being an active DIY'er, I even tried a 1500w direct drive conversion, and still run into occasional hills that leave me and the bike panting hard when reaching the top. This is while riding in a rolling coastal area though. I'm sure there are many areas where this setup will provide PLENTY of power. The fact is, a direct drive is more efficient than the other systems, but for my purposes, is hurting for the torque available with gears at lower speeds. Over about 15-20mph, the direct drives, all else being equal, are tough to beat.
What I've learned doing further research since, is that if I focus only on speeds below 20mph, where I find I spend all of my time, is that gears offer a lot more performance. This accelerating from a stop, or while climbing hills.
From a strictly personal standpoint, I don't care for the idea of the mid drive, mostly due to the stresses imposed on the chain drive system and the fact I don't do enough off road to justify their ability to climb at low speeds.
That leaves a geared hub system. I will know more here soon, as I have a top of the line MAC 12t hub already laced up on a rim, just waiting for me to have the time to sit down and do the conversion....
Gears for the hub drives are available, but they don't wear quickly under most circumstances. How tough they are to change will depend on how handy you are. -Al