Unnecessarily complicated? Qantas SC/points earn, the "Simpler and Fairer" system. There is no contest. The explanation of the detail on the QF website is long winded and still confusing. Making it tough to find by hiding it behind calculators is ridiculous. Determining the earning class requires a degree; with partner airlines, it's a third degree of pain for some airlines, especially if Business and First Class buckets fall into different earns depending on which sector is being flown (and which sectors these are aren't well defined). And if the route network - Qantas or partners - changes, the system isn't very adaptable to such changes, e.g. either it'll be uncertain what the earn is, there is no earn possible, or it'll be unfairly low because it isn't covered by the zone system.
I contend that there is no other frequent flyer programme in the entire world whose algorithm to determine the earn of status and points is more complicated than that of Qantas.
Not sure if things have changed, but Star Alliance status and points earn can be unnecessarily complicated when codeshares are involved, especially in Economy or Premium Economy classes. This is because the bucket to for earn is based on the operating carrier, not the marketing one. So let's say you purchase a ticket marketed by LH on a flight operated by UA. The LH ticket says your bucket is H. If this were oneworld, you go to your earn table and look up Lufthansa, then find where the H bucket is, and there you go. But in Star Alliance, the LH H bucket seat you have may be a different bucket when sold by UA, the latter being the operating carrier, e.g. your LH H bucket seat might be a Q bucket seat on UA. Your earn is based on looking up United Airlines and then finding Q bucket. Which marketing carrier bucket maps to which operating carrier bucket? Who knows.... certainly not displayed at point of sale.
I'm actually still a bit confused by Velocity's complimentary status for Gold/Platinum for the partner hotel and car companies, i.e. if you maintain your status, do you get to enjoy another 12 months of partner status; if you maintain your status, can you switch partner programmes; if you drop your status (e.g. Platinum to Gold) or upgrade (e.g. Gold to Platinum), do you get a new 12 months of status in a partner programme; if you upgrade your status to Platinum, then drop, but then later upgrade again back to Platinum (say after a few years), do you get a new 12 months of status in a partner programme, even if you have nominated that partner status previously? The Velocity website and T&Cs don't seem to make all these clear.
