The tadpole trikes are mostly pretty low and perhaps difficult for an older, heavier person to get on and off. The Sun EZ-3 trikes are higher...seating position is kinda like driving a car, where the tadpoles are more like go-karts. I have an EZ-3AX, which is a little sportier, a little lighter, and has more gears than the SX (and costs about twice as much, as I recall).
http://www.sunbicycles.com/sun/index.htm