You really need to define what you are doing and use then look for the right tool. Machetes are great for lighter vegetation and stuff under 1-2"...beyond that you may need a heavier chopper. The problem with a heavier chopper is that they are...well...heavier

Fatigue will play a big role. I say this, because if you've ever used a machete to clear a trail, you get pretty worn out with that it's a lot lighter than most 1/4" choppers.
Before you start shelling out cash on a mega 1/4 or 5/16" behemoth chopper, try getting your Ontario convexed...that may improve chopping (awaiting a modified 12" Ontario by Brian Andrews

). If you constantly chopping into thicker, harder woods, you need a tougher edge.
I need to take a new photo (Ilbruche now has my Becker Brute), but Bill Siegle makes some excellent choppers; if you don't need a pointy tip, Bark River's Golok is a masterpiece that chops and battens like no tomorrow. I have an older Livesay RTAK and it's a great chopper, so Ontario's may be okay (if it doesn't break on you

).
BRKT Golok
Fehrman; BRKT EVO-1; Siegle; Livesay RTAK; Browning Barker-Crowell
Somebody mentioned Valiant Goloks and they are also excellent heavier choppers...thick and convexed.
It's easier to recommend the right tool if you define what your requirements are...
ROCK6