thieliste - while you’re waiting for hands-on experience to chime in, I can provide some history.
Early-on (1978 model 03) we discovered the deleterious effects of eddy currents, first in steel driver baskets and later in aluminum voice coil formers. Part of that exploration over the years included binding posts. Either in direct power transmission or the secondary effects of changing magnetic fields, back-currents are generated from reflections and discontinuities along and near the signal path. Best practice is to keep cross-sectional geometry and resistances as even and smooth as possible to avoid distortion. Thiel kept its plastic-capped binding posts a very long time, and reviewers consistently took pot-shots for their ’RadioShack cheapness’. Fact is they weren’t cheap, and they outperformed most bigger, bulkier, brass rigs.
Somewhere around the CS1.6, Thiel converted to big, brass, gold-plated posts to praise from reviewers. I haven’t directly compared their sound quality to the ’old style’, but I will. I did hear that Kathy deemed the change as more politically expedient than trying to educate reviewers, dealers and customers.
Note that some of the high end posts have plastic caps. Danny Richie of GR-Research invented and sells a tube connector for the reasons outlined above. Some amp companies tried and rejected big metal posts.
My recommendation is something with approximately similar cross-section and conductivity to your cables and/or internal speaker wiring to avoid electrical reflections and resulting eddy currents. Copper would be a plus. A disadvantage to gold is the typical nickel under-plating which many consider to sound bad. Simple, small and high conductivity are pluses of course.