Generally, big Internal Gear Hub proponent here. That said, here's a 47 page, 696 entry thread titled 'Shimano Alfine 11 - Longer term reliability' from our friends at CTC [...]
I'd specify the derailleur drivetrain, but that's just me. If you go for the Shimano Alfine 11, make sure it's the latest, improved SG7001-11 release (if Helix purchased the hubs some time back, they probably won't be).
I'll get the Alfine, it is neat and clean for a folding, and the tensioner is more compact.
The derailleur tensioner is bigger and gets less ground clearance, quite noticeable for small wheels. And when folding, the tensioner faces additional challenges depending on the gear you are in. Looks like Helix has solved this, I just prefer the simplicity that a single chain geometry brings.
I also had my concerns on the Alfine 11 and checked with Peter recently, he had already done his due diligences on this topic and had checked directly with Shimano and their trading company. They have both confirmed that the Alfine is very reliable and has had very few warranty claims, that most reliability issues come from improper installation such as belt drive setups where the belt is too tight and it over tensions the Alfine bearings.