Not sure there is a best since what one finds to be the best is pretty subjective. I like the DGT XL and DGT NA. They are easy to set and seem to be well built. However, they are plastic and don't show seconds on the clock until under a certain time. I think the DGT 3000 shows seconds and would likely be a nice clock as well.
Recently I've been picking up the new clock by Wholesale chess, based on one of the Chinese LEAP clocks. It is very similar to the DGT line, has some features that are nice, and are also easy to set. Again, they are plastic and just a little less solid than the DGT. However, price is lower than the DGT clocks mentioned (not including shipping).
A lot of people like the Chronos clocks and the Z-Mart II clocks seem pretty popular. Both have pretty solid metal bodies but seem a little harder to set (though once you learn how it probably isn't that hard).
what is the best chess clock?