It's funny you should ask because it's asked a lot and for all the searching I've done, there's not a single clear, comprehensive comparison all in one place. I should weigh my parts when I have one of the Contenders apart, but I forget every time.
The bottom line is that the Encore is "bigger and heavier" (sorry, I don't have dimensions and weights) and will handle a lot more pressure (won't go into the whole back-thrust, area of a circle thing), meaning that the Contender won't handle the 308W, '06, 260 Rem., etc. The Contender is generally meant for pistol cartridges and certain low pressure rounds (30-30, 7-Waters, etc.).
Physically and mechanically, I believe the two are built the same, just that the Encore is beefier.
My preference for the Contender is for the tiny little, lightweight action which makes an amazingly light and handy rifle which is still perfectly capable in the hunting fields from squirrel to deer and a real pleasure to just goof off with. Some guys load this little gem up with several pounds of laminated wood and some serious optics to take advantage of the accuracy potential, but my buttons get pushed more by the wispy nature of a 5# rifle that is not a compromise in terms of accuracy and hunting capability. There are a lot of people who want to push the limits and get right up against the line on pressure on the Contender, even some who make a living doing so, but I think I'd get an Encore if I wanted to do more than a 30-30 or 357 Max can do in a Contender.
No criticism on the different ways people use the Contender. I just like the really light and handy nature of it when chambered for mild but hunting-capable chamberings in super-light carbines. They are harder to shoo well, but that is much more a matter of the shooter adapting than a short-coming on the gun. I get reminded of that every time I shoot one while trying to wring out load development. two touching, then three, then one off a bit and another touching that one,.... I really, really have to be on top of things to shoot mine well, but I don't shoot nearly enough these days.