If you can find one (NLA new) a Roland EV-7. Long sweep and smooth linear slope. 10K pot. Also, Yamaha FC7. Polarity (tip/ring) backward from Roland, in other words on the Roland the wiper is measured by the tip and on the Yamaha the wiper is measured by the ring ( I may have this backwards). What does this mean; many have reported erratic linear slope, depending on what the requirements of the keyboard are vs. what the pedal provides. Easy fix though. Just purchase the below, hooking up the red to the black and this will switch the tip/ring and most of the time produce the linear slope needed.
The Yamaha FC7 has the largest sweep of the two, but the EV7 does have an acceptable long sweep to play hammond organ. I own both pedals, both are acceptable. Stay away from the Roland EV-5. The pedal doesn't have a long enough sweep to actually produce any real expression, especially when playing organ.