The upside of the contender is it's a compact package and since it's been around for so long there is a huge market of used barrels out there. The downside is that due to the design of the frame you are limited in what backthrust the action can handle. It's important to understand the issue is backthrust as you can use the .223 and associated rounds that have a .378" casehead and operate them at full pressure. But when you increase the diameter of the cartridge, you have to reduce pressure. You can't use any of the rounds that use a .473" casehead and operate them at 65 kpsi (you can in the encore) but there are wildcats that run similar rounds at pressure that the contender can handle.
The encore can handle most any chambering you want to use, but it's a bulkier package.
Personally I prefer the compactness of the contender and can live with the pressure limitations of the frame. I had an encore but sold it before even firing it as I just didn't care for the bulkiness.
