I've got a bk9 that I use for this (more batoning now, since I got a folding saw), and it works great. It also out chops my (no name brand) hatchet, and like mentioned it does do small knife tasks much better than you'd think, which is great.
And while I'm confident I could chop down just about any size tree with it, I agree that once you get up around 5-6in, its WAY more efficient to saw, or use an axe.
The Ontario sp10 should be a big heavy chopper on a budget, the junglas is a proven performer as well (but is about 2x the price of the Becker). Then the khukri options are great for dedicate chopping, as are machetes depending on your location (14in bolo, or the baronyx machete) are heavy hitters. Then there are the larger bark river knives (bravo III).
Anyway, any of those would be good, it just depends on what you're looking for, and what your budget is.