I have both the Corona and the EP Concept. I really enjoy both of them, but for different reasons.
The Corona is as tough as nails, and was my primary trainer when I was just starting out. I remember crashing at least 10 times in a row the first day I had it. After straightening the boom that night I flew it again the next day, and flew (crashed) many more times before finally breaking the boom in two. That set me back $2 for an aluminum arrow of the same size at the local archery shop. If you've never flown, the Corona will serve you well.
The EP Concept is a finiky machine, but after sorting out it's various issues it is a great flying heli. Nothing serious, mind you, but it doesn't fall into place as easily as the Corona does. It flys much nicer due to the increased weight and collective pitch. It's also larger (rotor diameter), and seems to settle into a hover much nicer. Parts are not really a big issue right now, contrary to popular opinion. What Tower doesn't have in stock can be bought directly from Japan -- the Concept is much more popular there. The parts do not come as cheaply as do the Coronas, however.
So I'd suggest keeping the Concept as your 2nd heli, and getting a Corona to learn on if money allows. I've never had an Eco, but from what I've read I'm sure its more fragile than the Corona.
For a simple video of the Concept in-flight, visit (right click and "Save Target As"):
http://rclibrary.com/vids/EP_Concept.mpg (45 MB)
This is just some hovering in the back yard, as I'm a fairly new pilot myself. Not really worth downloading if you don't have broadband. Just thought you may want to see how one flys once it's dialed in.
Hope this helps,