I've been using a Mainline rear-tine tiller since the mid-80's, which I bought used. The tines rotate forward, the handle & wheel direction are reversible for using other attachments, and it has 3 speeds in either direction. Mainline was allegedly just BCS tillers being sold under a different name, when they were first imported. It's a tank of a machine; it has eaten bricks, large rocks, dog stakes, and a buried pence post, without breaking. The tines have been changed twice, and the clutch needs service now... but it still runs reliably.
But as others have already pointed out, breaking ground with forward-rotating tines can be like holding a tiger by the tail. The tiller has a tendency to dig in & jump when it hits hard ground, jerking you along with it. Regardless, that is what I did year after year, because I thought it was the only way I could cultivate 10,000+ square feet of garden. I accidentally learned (only a couple years ago) that I was doing it wrong, when the throttle cable slipped; that provided the engine is strong enough (in this case, 8 HP Acme) breaking ground is more manageable when running at just above idle. Once the surface is broken a couple inches down, I can turn up the RPM without the tiller jumping (as much). Breaking sod would still be a guaranteed sore back, though. The Mainline has a lightweight aluminum-alloy chassis; perhaps the heavier cast-iron chassis that Troybilt brags about really is more manageable.
Forward-rotating tines tend to walk, and require multiple passes to produce a good planting bed... but they also throw rocks & debris behind them where they can be picked up, and tend to gradually level out the soil. I also find that when attempting to turn under large amounts of organic matter, forward-rotating tines do so evenly, without clogging.
Counter-rotating tines will break ground without pulling your arms out of their sockets, and will do a better & faster job breaking down clods into a smooth planting bed - especially with heavy soil. But because their rotation is in opposition to the wheels, they tend to bog down when digging deeper. When this happens, it tends to create hills & holes, which if the wheel base is long enough, are further accentuated in successive passes & gradually create uneven ground. Counter-rotating tines also tend to kick any large objects they encounter forward, where it can be hit again & again... increasing the chance of jamming or damaging the tiller. And for the same reason, when attempting to turn under sod or large amounts of organic matter, it will tend to build up in piles in front of the tiller box, to the point where it will either bog down the tiller or leave deep ruts in the ground.
So IMO the best rear-tine tiller would be one of the models with reversible tine direction, giving you the best of both worlds. There are not that many of them, usually only 1-2 models per manufacturer. The one thing they almost all have in common, which I don't like, is only one forward speed. Because that one speed may or may not be to your liking, it would be wise to "try before you buy". BCS tillers offer more speeds, but they are really two-wheeled tractors meant for heavy-duty commercial use, and priced accordingly.
Regardless of what tiller you choose, ask the seller how the tiller will be protected if it hits an unbreakable object; and if it uses shear pins, buy a handful. Nothing is worse than having to stop in the middle of tilling, to run for parts (spoken from experience). It might also be wise to stock up on extra things like air filters, which can be hard to find when the model becomes obsolete 10 years or so down the line (I'm looking at you, Troybilt & Earthquake).
One thing I have never understood about self-propelled rear-tine tillers is how their power transfer is designed. The gear box on the tiller is always centrally located, which creates a "blind spot" to keep the tines from hitting the gear box - and leaves a line of untouched soil in the center of the tilled area. This is particularly noticeable when breaking sod or heavy weed growth. So regardless of the direction of tine travel, that "hill" of soil must be broken down by successive passes. IMO it would have been smarter to mount the gear box on the side of the tiller box, so tines could be mounted overlapping on a single shaft, and would till evenly over the entire tiller width. That is the design I see on some tractor-mounted tillers.
A friend gave me a small front-tine Earthquake tiller, to keep if I could fix it - which I did. It is 2-cycle, which I would ordinarily avoid... but the price was right.
I wouldn't even think about breaking ground with it, and weeding anything beyond a small area is a back-breaking chore (as I found out last year).
But it comes in handy for deep-digging a small bed, works well on soft or sandy soil (such as DD's garden), and is small enough to bring into the garden for late-season planting. All tillers come in handy when used for purposes which play to their strengths.
www.troybilt.com
