Thom,
Brilliant post. Thank you very much for saving me alot of typing!
The Bent stepups are indeed excellent, though as Thom implied there is no one "best" trannie. Adjusting the reflected impedance on the secondary side (very easy with the Bent's) is vitally important, but even then you have the issue of the primary side impedance interacting with the cartridge. I suppose this is why (IME) some trannies work better than others with a particular cartridge even after reflected impedance is optimized.
As Thom also implied, using trannies well involves a lot of work. LOMC's are extremely sensitive to reflected secondary side impedance. Those who claim trannies have non-flat frequency response simply haven't done the necessary work.
We spent dozens of hours swapping cheap resistors. Finding the optimum value for a cartridge almost always requires doubling up resistors on each trannie. (This allows much finer gradation of resistance values.) Having done all that, we then spent hundreds of dollars on multiple sets of high quality resistors. I'll discuss those results in another post if anyone cares. The results with every cartridge were always an even frequency balance.
At ultimate performance levels, however, it is now my belief that a properly implemented gain stage will outplay any trannie. A transformer must, by its nature, diminish amplitudes and smooth waveforms. The effect in a good trannie may be very slight, but it cannot be eliminated. This means a diminishment of dynamics and a rounding of notes (bloat, in plain language). My new preamp/phono stage is built as Hi5harry described, FET followed by RIAA circuit followed by tubes. It easily outplays the Bent's and every other tranny I've heard. I have a friend who owns nearly 20 different stepups. He's used some of them for over 30 years. Once he got his new preamp (same as mine) they all went into the closet.
Beating the Bent's and Cotters takes a large outlay however. If you aren't able to spend $6K+ on a privately built preamp or $10K+ on a commercial one, the trannie route will often do a better job, provided you're willing to do the work.