Hi Hoodoo,
If you're just doing light chopping and brush clearing around the house, the 18" Ontario works real good. I've got 5 or 6 of these things and I keep them sharp. I don't have a favorite out of the crowd and just use whichever is sharper or handy at the moment.
I sharpen cheap machetes on a bench belt sander with a worn out belt, works good as long as you don't hold them down too long and get them too hot. In the jungle I use a flat diamond hone...takes a little longer but does the job.
I haven't used the 12" too much so I can't comment. An acquaintance of mine, Morgan Smith, swears by a 12" machete for jungle use. Morgan knows his stuff too, since he's run over 50 expeditions into SA and also set up several foreign government jungle survival training schools.
I haven't used the Barteaux at all. If you're going to move on to heavier chopping, then a heavier blade like the RTAK or RCM and others on the market work well for this. The handles on most of these custom machetes are also a lot more comfortable.
I think Steve Dick said it best in his latest article concerning big blades. The RTAK and others like it are designed as 'Trail Blades' - I think of them as a crossover between a machete and a useable work knife.
I've never had a lot of fatigue problems with the Ontario when using them for their designed work but if you get to bangin' in heavy stuff you will feel the shock.
A lot of folks try to use a machete the same way they do regular knives. In my opinion, it's a totally different concept. When you watch the Indians of SA use them, they always take a full swing with the spine of the machete almost laying on their back when they start the motion. Not a hard fast swing, but a long, smooth, full motion swing.
I've also seen them mow grass with these things...amazing.
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Randall's Adventure & Training
jeff@jungletraining.com