I have two bikes, a Viking Ego with a six speed deraileur and a Brompton with both a three speed hub and two speed derailleur.
I bought the Brompton in 2004 and it still has the original chain, sprockets, and hub gear, which still functions OK as does the derailleur, there appears to be no way that you can lubricate the three speed hub gear, and the idler gears of the derailleur need regular cleaning, as being so close to the ground they get clogged with dirt and then it won't shift gear, but that is easily remedied.
The other bike the Viking has a derailleur which seems to work fine so long as you don't ride through fallen leaves and clog up the gear cluster.
To me they both seem perfectly satisfactory, though admittedly I am no longer strong enough to stress either system all that much!
My preference? for ease of use the click stop Shimano on the Viking.
No fuss!