If we're talking factory, I really like the handle on Fat Handle Techs. Otherwise, the stuff CooncatBob is making takes the cake.
Red Tip and Durham Duplex.
OK - I'm going to cheat here and nominate the Gem 1912 SE razor with the six-sided handle with heavy engraving. The balance is just right and the engraving offers great grip when wet as well as being very attractive. This is further enhanced with two rings cut into the bottom of the shaft which help excess water drain off the handle and gives the bottom finger something further to grip on to. However I find that it is the six-sided shaft that enables me to comfortably "lock" the razor between my fingers in a manner which I simply can't do with any other razor. It's a great idea which I don't think ever appeared on a DE razor but it is so unmistakably a sign of a Gem / Ever-ready that I wonder if the company had the idea copyrighted. Here's a great image grabbed from an earlier B&B post (with thanks to the original poster).
...It's a great idea which I don't think ever appeared on a DE razor .....
I like the HD handle, but I really like the 1904 handle.
I like the handle on the EJ Georgian so much I ended up getting the whole set of them.
Ball End Old Type, of which I have three, hands down. I don't think anything made by Gillette afterwards was an improvement with the exception of the Ball End NEW. Although I primarily use single edge razors as my daily shaver, when I do grab a DE it's usually one of the Ball End's, either the NEW or Old Type. I just love the feel and balance from the weight in the handle.