Wow,
@r04DiE seems to be my alter ego.
I'm in the process of researching the same thing. Here's my current research and thinking. Partly to give
@r04DiE the benefit of my searches, and partly to give People Who Know the chance to point out that I'm an idiot.
Best in class dynohub seems to be SON. There are two main variants, the SON 28 and the SON Delux. The delux was designed for 20" wheels and has lower power output (actually a different power output curve). By all reports not so good if you want to run lights and charge things at the same time. But it does have (indetectably) lower resistance than the 28.
Alternatives are Shutter Precision (SP) and Shimano. Have to admit I haven't looked in to SP so much.
The appropriate Shimano model for road riding is the N80. THere's also an N30 but I read reports that it has significantly higher resistance, and just isn't as good.
Rightly or wrongly I discounted SP and other Shimano models so it's down to SON28 vs Shimano N80.
Resistance: I think that the SON has marginally (but by all reports indistinguishable to humans) lower resistance. And the resistance overall of a hub when riding has been described as "the square root of f-all". I still remain a bit concerned that a weeny bit of extra resistance over multiple 100s of km could be the straw that breaks the camel's back. But I suppose that could also equate to carrying an extra pork pie. It still preys on my mind a bit.
Servicing: SON seems to require servicing after 50,000 km. Which is, in my book, never. Shimano servicing consists of having the innards completely replaced. The dynamo is going to outlast the rim easily (if using rim brakes, that is).
Price: SON costs a heap more than Shimano.
They all come in disk brake versions, I think. Not sure, because that's not a requirement of mine.
On balance I've decided to go for Shimano N80 because the advantages of a SON seem marginal, and the price jump is big for not all that much. The SONs do look much nicer tho. Hmmm...
Lights. There's a big choice, and some have built in cache batteries or capacitors to give you stand lights. Other features include sensors that switch themselves on and off, and various other goodies. I've decided to push the boat out on the light and get one with built in USB charging facilities and lots of bells and whistles. This is the Busch and Muller Lumotec IQ2 Luxos U. At the rear there is again quite a wide choice.
Wiring. In the old days you attached a bottle dynamo to the seat stay and tightened a little grub screw that dug into the frame and everything used the frame for earth, and you had a single wire. These days I think you use two core wire. I'm still concerned that if I buy all this stuff the wiring project may have extra demons in it that I haven't foreseen and I end up having to buy more stuff, and my bike ends up looking like a half unravelled piece of knitting. I've looked at the Shimano N80 manuals and they seem to only show you how to connect up a front light, not rear.
USB charging: This subject seems massively complicated and confusing. It requires the purchase of a "thing" (e-Werk or Igaro D1 or other) that converts the dynamo output to an acceptable voltage for USB. I've not been able to make any sense out of it at all, and I fear that it may make the wiring even more of a rat's nest. That's why I've gone for a front light with this built in.
I'll be buying from Spa because I'm a regular customer and trust them and I don't have (and have no intention of acquiring) wheel building skills myself. My current thinking (not pulled the trigger yet) is:
I'll be sticking with 32H rims because that's what I have at the moment, and it doesn't seem to be at all broke. I've never had problems with spokes, despite being a 92kg porker.
