4 Star
 

Having had both the Easy Sport and a 4*.40, I say go with the 4*.

The Easy Sport is a great plane and I enjoy flying mine (ARF version). It's easier to fly then the 4*, but I don't think it's much different in performance than the Avistar. Might not be enough of a new challenge for you.

The 4* though would be a great next step. Low wing, tail dragger and a good step up in performance. This is my favorite plane. If I were to do it over I'd also go with the .60 size. Laser cut wood and only about $50 more than the .40 size if you go with a .75 2 stroke engine. Much more bang for the buck!

Second Airplane
 

I started with a Avistar then got a Mid Star. The Mid Star flew just like Avistar. My third plane is a Tower Kaos. It was an easy an kit and it flys like in on rails.:)

2nd plane options
 

Are you thinking of getting a warbird down the road. I think that you have probably read that they need some speed on to land or they tip stall. A 4* needs to slow to a slow walk to come down or it just keeps cruising. It can teach you how to fly fast, but it can't teach you how to land fast. Thats why I suggested a WM Rambler 45, or a Tiger 2. They can fly slow or fast and land slow or fast. A 4* was in our funfly and it was unable to be a serious contestant in the limbo contest because of its floaty characteristics.

Second Airplane
 

For my seconde plane I flew Pt-19. It is a good flying plane. Like all tail draggers it might go to the right. It is also easy to see. It comes in all sizes.