For anything more than a 3-speed, the cost might be an issue.
I only have direct experience with the Shimano Nexus and Alfine 8 speeds and Sturmey S3X fixed 3 speed.
The Shimano units have proved to be extremely reliable, nearly maintenance free (excepting the recommended re-lube every 5-10k miles), and dead simple to use. Shifter options include
trigger shifters and
grip shift (flat bar) and
bar-end or
brifter (drop bar).
An IGH conversion is generally pretty easy to do if you are comfortable working on bikes. The frame will either need to have horizontal dropouts or an eccentric BB, or you'll have to use a
chain tensioner.
Quite often, you will find that a pre-build rear wheel will cost about the same as the hub alone, so that would be something to look into.
No matter what, the project will cost some money.
I'm currently looking into 5,7 and 8 speed options for my second bike, and the Sturmey Archer hubs look like appealing options.