I have both an IGH and derailleur bike, English Raleigh. The old SA English hub sees rain here a lot. No problem. Only maintenance is oil squirt once in a while. I seems to me much more efficient that the Shimano Nexus 7-speed I once had. I don't do hills here, and maybe if I did, my opinion would be different, but this works for me, well enough. Its not hard to take off a rear tire either, just one more step.
That said, I do like my derailleur bike. If I had to make choice and have only one bike, I would go with a derailleur.