I have a trike. It's not a Sun it's Catrike Road. I only got it in November. I've ridden about 50 miles so far this year. So I don't have a lot of experience on it, but I suspect that it's gonna be one sweet summer for riding. Man is this trike nice. It's not as fast as my EZ Sport, but I can climb hills very easily and so far this trike is the best thing since sliced bread.
I suggest you try riding several different models before deciding on what to get. When I did I found some interesting differences. I didn't ride a Sun EZ-3SX however. I tested the Catrike, Greenspeed, and Wizwheelz. The thing is you may be able to find a better trike used. That would help keep the cost down.