Originally Posted by
Spasticteapot
The derailleur system has a wider gear range, smaller spacing between the gears, supports a wide range of convenient shifters, and is far more efficient than an IGH....but the latter is cheaper, is almost completely immune to rain and salt, and is far cheaper and simpler to maintain.
For the sake of comparison I've owned lots of derailleur equipped bikes. I currently own 3 derailleur bikes and 3 bikes with Shimano IGHs and 2 Rohloff bikes.
Efficiency
IGHs and derailleurs at the Nexus8/Alfine/Rohloff/LX/XT/105 end of the quality spectrum do not exhibit differences in efficiency that are dramatically different. This is not to say they are identical, but the differences are in the few % range. If you use your bike in all weather conditions and for long periods of time my experience is the performance differential disappears and can even switch in favour of the IGH as things get dirty.
Gear Range/Spacing
It's a simple thing to swap out cassettes on a derailleur bike to change your gears significantly. Although I know of no one personally who actually does this in practice. Just about everyone I know is interested in a wide range cassette and not as fussed about having tight gear spacing. So once they get their bikes setup with an 11-32/34 cassette they don't change it for different rides.
IGHs have fixed gear ranges and spacing [except the CVT IGHs]. So you like it or you don't.
Rohloff - wide gear range equivalent to a MTB 3 x 9 drivetrain with equal spacing between gears.
Shimano IGHs - less gear range than a MTB 3 x 9 drivetrain, but you can use a double front chainring to get a wide range solution. For city use I find the Shimano IGHs work well with just 8 gears. I am experimenting with a Bike Friday touring bike to see if I can get by with just 8 gears touring in the mtns. I do have the option of using a double chainring on that bike with friction shifting to get a wide gear range, but I'd like to just have the IGH and keep the bike as simple as possible.
Cost
Is difficult to assess because it requires a long term life cycle analysis to really capture the benefit of the high quality IGHs. As an example I can get derailleur parts quite cheaply, but I need to maintain/replace them in challenging environments frequently. OTOH - I'll still be running the same Rohloff hub in 20 years with minimal maintenance.
If you value the lowest upfront cost than it's very hard to beat a derailleur drivetrain. They are so ubiquitous you can almost get the parts for next to nothing if you are not fussy about it. Even the higher quality components can be had on sale if you are patient.
If you value your time more highly and want a simple drivetrain that isn't going to need much thought/attention an IGH is very attractive.
If you have a long term view of things and plan to ride your bike a lot a Rohloff hub can cost less/km than a derailleur drivetrain. You can even realistically expect to pass the hub onto your kids for them to use. However, the upfront cost is high.
Maintenance
I did a dirt road tour up north that started dry and ended up being a multi-day mudfest. At the start I was meeting riders on derailleur bikes that had shifting issues simply because the dry dirt road was very dusty. My Rohloff bike shifter fine and needed no attention. The following days of mud riding were not super fun so I would just jump off my bike at days end and crawl into my tent. I did no maintenance to the bike. My Rohloff bike shifted and pedaled as well the last day as it did the first day when the bike was clean. My entire maintenance on that hub in the year I've owned it was one 10 min oil change.
Ultimately the fact is both derailleurs and IGHs work very well. They are different and have pros and cons. I would suggest that investing in a Rohloff or even a Shimano IGH makes sense for everyone. On the other hand the attitude that IGHs are inefficient/heavy/etc... isn't a very realistic assessment of these components.