A decent Shimano is "Okay" cheap and plentiful and last long enough not to be a total PITA to be changing them out all the time. Personally I have had the best luck buying high end retro freewheels "new in box" that are a couple decades old and sold as vintage collectors items. You can get down to a 12t on the bottom cog with them. Watch your threads not all of the old ones use the standard thread size we are used to. There is also one brand that was like the best of the best of the old ones with swap-able cogs for custom arrangements and is rebuild-able and were the ones that were made the longest before they finally quite making them after the modern cassette hubs became well established. Can't remember that name brand off the top of my head but I've got a box full of them along with cog sets for them along with spare parts and rebuild kits for them that I have snatched up over the years. Might have to wander out to the shop and look in that box and re-jog my memory, crazy I should have that brand name at the top of my memory but just isn't coming to me right now for some reason.