My only complaint on machetes, and it is much less critical than the advice above is to find something with wood grips over weak plastic or faux rubber. My hand does not fatigue as fast with a wood handle. The others rattle my hand something fierce.
I have found that wrapping the handle with cloth tape, like that used on tennis rackets, helps a lot. Not having to grip so hard to hang on keeps the hand from tiring so fast.
If the handle is wood or slick plastic scraping tit with the edge of a knife to roughen it also helps.
A lanyard sized so you can loop it around your little finger, up the palm ,and around the hand to the attachment point on the handle further steadies the hand. This arrangement is used on night sticks and improves the grip while allowing you to easily let go.
I have found the Trimantina and USGI, usually made by Ontario as I understand it, units to be solid and workable.
If you do try to cut thicker and harder wood you need to came at it at an angle and take off thinner pieces so the blade doesn't get stuck.