That is going to be a matter of opinion. Custom made ukuleles from many different luthiers run in the thousands of dollars.
In general, solid topped ukuleles, as opposed to 'plywood' laminates, are considered the best. Vintage instruments are also highly sought after. A vintage C.F. Martin Ukulele from the 20's or 30's can bring $4,000 easily. Many current musicians use the Fender ukulele because they have used Fendor Guitars for so long.
Most would say that a Koa wood ukulele made by one of the small Hawaiian companies that still individually make their instruments is going to be top of the line.
You can find them all over the world. However, most agree that the best ukuleles are made in Hawaii. The quality of Ukuleles being made in the rest of the world is improving. CF Martin continues to make some of the best and they are found in Pennsylvania, USA.
"Ukuleles" is a plural noun.
Electric ukuleles can be purchased from many different online stores. Some examples of stores that sell electric ukuleles include Sweetwater and Austin Bazaar.
Their web site does not show any ukuleles being for sale.
One source would be eBay. Starter ukuleles are available for about 10 pounds. Real Music and Purple Turtle are a couple of shops that carry ukuleles.
no
No, they do not require a truss rod. Some of the Banjoleles have them installed, but they aren't required.
Stringed Lute
Harmony ukuleles where made in the US. They name was sold in the 1970s to be used on Asian produced guitars.
If you can locate a Guitar Center, check it out.
Ukuleles are commonly tuned G4 C4 E4 A4, the baritone ukuleles are tuned D3 G3 B3 E4.
All ukuleles are strung with the 1st and 4th strings on the outside. They go in order 1, 2, 3 and 4.