I have a 7 speed IGH Nexus on my Breezer and an 18 speed on my Giant Rapid, and ride a work bike that has a 3 speed Nexus hub.
The hubs don't need maintenance. Some will say otherwise and maybe they have some other experience, but i've never oiled my 7 speed hub and have about 11k miles on it (my odometer died about 2 yrs ago). the only maintenance is with the chain. Use kevlar belted tires to reduce the chances of a flat and you'll love the IGH.
My Giant is a faster bike, anyway you slice it. That's fun. But, I need to carefully strap my pants and I don't have fenders on the bike. It's a road bike, so it should be fast, but it's my fair weather bike only.
Derailers, imo, require more tuning and I don't like the exposed chain. You can drop a chain much much more easily that you will on an IGH bike. That said, if you are just looking at 3 speeds, which I think is a good option (my work 3sp bike is fine when I go up a fairly steep but short hill), you could compare that to a 7, 8, or 9 speed rear derailer and a single chainring--no double or triple--on the front sproket. A 1x9 is nice, efficient and has decent range. Rear derailers are ok with me--the chain doesn't drop. My 7 speed hub can go up any hill, almost as readily as my 18 speed. I don't notice the difference, but I don't live near a mountain.
But, for me, a bike with a chainguard is the one I'll always ride the most. Chainguards and fenders are key for bike riding on most days in Cleveland.