QUOTE(etigge @ Dec 12 2015, 08:54 AM)
When SRAM started, they don't have an internal gear division. They then took over SACHS. Those days, only Sturmey Archers and Sachs are the main players. Sturmey Archers is around even when I was riding a Raleigh Chopper 1977 (also 3 speed) and they lasted till today. After SRAM took over Sachs, the price skyrocketed because of their branding and not necessary because of their expertise. So, why limit yourself to a SRAM ?
Sturmey Archers actually have 5 and 8 speed (if I can recall). The 5 speed shares the same interior measurements with the 3 speed. That means if you can buy the 5 speed innards ( probably from UK ), you can fit it into a 3 speed Brompton hub. SO, that converts the 6 speed into 10 speed. Nobody here does that here. I have actually bought an old SA hubs and dis-assembled it and rebuilt it and it is actually not that hard. Alas, Brompton owners don't trust non-Brompton owners to do their precious bikes so I never service for anyone before.
I would rather go for the Shimano Alfine which comes in 8 speed (very cheap nowadays) but the 11 speed would cover more ratios. A cheaper option will be the Shimano Nexus which is 8 speed. Best option of all, I would say IMO

is to hunt for a used Rohloff in eBay.

14 speed which covers almost the entire 3 X 9 speed of the conventional FD and RD gearing systems. Also Rohloff are maintenance free!

Cheers!
Hey, I had a Chopper too! Five of us kids used to pile on the bike and we went places, with me doing the cycling! Haha
Yes there are options but I like the combination of cassette and hub. I had an Alfine hub before on two bikes, but it was heavy and there's always one ratio "missing" due to the gaps in the ratios. The SA 5 speed is apparently less reliable than the 3 speed. Funny though, the 3 speed Sachs in my Bromption shifts less smoothly than the current BWR hub, but the SRAM DD 3 speed is just as good plus you have the benefit of playing with more ratios to suit, and the hub is lighter. Rohloff would be amazing but the weight......