Here is an example of an high bottom bracket open cockpit design, the Bacchetta Corsa:
|Corsa - Open Cockpit steering|
Now as you can see the rider pictured here (myself) has fat sausages for legs. Because of the high bottom bracket (the height of the pedals from the ground basically) and the reclined position the thighs get in the way of the handlebars during turns. This means that when I want to make a tight turn I have to drop the inside leg off of the pedals so I can get the angle needed. This becomes annoying and prevents me from pedaling during turns, which means if I am going slow or uphill the turn is not easy.
|Raptobike - tiller steering|
Above is the Raptobike, with tiller steering. It also has a high BB relative to the seat height but the tiller steering won't hit my inside thigh. I have a Rans Vivo with tiller steering and I find it very easy to use. Though my elbows are in a closed position with the Vivo. This isn't as comfortable and my elbows sweat a bit over time. For a picture of how this looks, here is a rider on an M5.
|Anja on M5 Shockproof in Norway|
This can be changed by cutting down the stem, moving the handle bars closer to the legs and increasing the reach needed. There are pros and cons of this approach as the stem also moves in the direction opposite of the turn like a boat tiller. So by increasing the reach you also limit the final angle of the turn available due to reaching the limits of a given persons reach.
The net result of all of this verbiage is that due to my desire for high BB recumbents and my sausage legs, I find tiller steering more to my liking. But like all things in recumbent land, adjusting the particular steering to my own fit and expected usage is key to satisfaction.