BioPace and Ovaltech. I'll use Q Rings when/if the price comes down.
Be a lot easier with the Q rings' multiple mounting holes.

On a bent, your max pressure on the pedals comes later in the pedal stroke. So I set the rings so that the chain is coming onto the highest part af the ring about 45 degrees before full extension.

I have Biopace set this way on my exercycle, and a round ring of the same size.

When on the round, at a speed that has my heart rate around 140, and my legs just starting to burn, I can shift to the Bio and maintain the same speed with an HR of 135 and no burn. Shifting back to the round, HR goes back up and the burn comes back.

YMMV but I percieve the BioPace to be much smoother. When I was using round rings on a 'bent, I would notice how much easier it was to get a buttery smooth spin on an upright. So I started looking into the physics of pedalling in the different positions. Because of the orientation in relation to gravity, the weight of your legs works to increase the torque applied late in the pedal stroke. This makes your pedalling a bit choppy,as there is an accelleration late in the stroke. (Sort of like Biopace on an upright, but in reverse) Setting the Biopace to absorb this torque peak makes pedalling my 'bents feel as smooth as my uprights.