I have a bottle dynamo on my tourer and a Shimano hub generator on my everyday commuter.
The tourer setup is as good as any bottle dynamo can be, quality Nordlicht with rubber cap, bolted to a small, solid braze-on tab at the rear wheel, used with Marathon tyres with the relevant dynamo strip. I have used it in solid rain for hours and it works OK. I wouldnt trust it in snow, slush or sticky mud. Wiring the system reliably is tricky, I think dual wire circuits are easier to connect than using the bike frame.
The hub generator is faultless, works in all conditions without missing a beat for years. The only downside is that sevicing the bearings is a tricky and dangerous operation. If you break the small conductive ribbon there is no way of fixing it (is there?, if you know, please post it). Drag on the hub is not noticeable.
Both units output the same std 3 watts of power but the amount of illumination varies with the efficiency of the lamp. New LED units are far better than old bulb ones. Newer generations of LED are better than older LEDs.
I tried using an LED rear with a bulb front. When the bulb or connection goes, all the power is diverted to the rear and it blows. Is there a solution to this?