the traditional tapered plug bronze seacocks on my cape dory are going strong in their 21st year. Cape dory, alas, is no longer with us, but Spartan (who manufactured the seacocks) is still in business. I would recommend their seacock to anyone.
Maintenance isn''t that onerous, as long as the seacocks arent buried deep in a locker. Just disassemble them, clean, grease with a high quality waterproof grease (its the grease that actually seals out the water) and reassemble. do not over tighten, as this only forces out the grease. Needless to say, only service them when the boat is hauled.