The type of handle that you need for your tomahawk is going to depend on what kind of activity you are going to use it for. Wood-handled tomahawks tend to be the preference but both throwers and historical reenactors. Full-tang tomahawks (where the blade and the handle are the same piece of metal) can provide a remarkable amount of sturdiness, but suffer from a lack of shock absorption capabilities that can cause them to be quite fatiguing.
The great majority of Tomahawks on the market today feature synthetic, nylon-based plastic handles that are a generally good balance of weight, strength, and shock resistance. It also far less expensive to make a nylon handle than a full-metal handle, and those savings tend to get passed on to the consumer.