I own all three. Original Contender, G2, and Encore. All are fine guns, however I prefer the G2. All are outfitted w/ Pachmayr grips. On the original the fit of the forend looks better around the hinge pin area, the G2 has a gap there that doesn't look quite right to me, I'm undecided on the originals "artwork" on the receiver sides vs. the "clean" look of the G2/Encore. Years ago quite a few people paid good money to have the sides of their Contender smoothed. That's it as far as looks go, now for performance...Of course the Encore has the edge on performance, but the Original/G2 will get the job done well on anything you will ever hunt. The G2/Encore are available in stainless, where the original never was, they had a silver finish available ( I believe it was called Armalloy ?). On the original the blued barrels/receivers would not interchange with the "silver" versions. While many blued originals were made and as you've already found out barrels are plentiful and will interchange with the G2, the same cannot be said for the silver ones. The G2/Encore does allow for interchanging between blued and stainless components within their respective lines. Triggers on all can be set up to for excellent performance. The original Contender is harder to break open, and the trigger guard "spur" doesn't have as much clearance for your fingers, this can be a problem with big hands, hard recoil, gloves,etc. The hammer on the original/G2 can istantly select between rimfire/centerfire, and this can be used as an additional safety device, the Encore requires tools and a little more time to select between rimfire/centerfire. The Encore Pro Hunter has a hammer with an adjustable offset to clear scopes, all other require you to purchase an attachment for this. The Encore has a larger frame which doesn't fit small hands as well, but as already stated, a set of custom grips does help a goog bit. The Encore can also be configured as a rifle, shotgun, and muzzleloader. The Contenders only a rifle that will only work for lower pressure cartridges. It pretty much comes down to your preference, what feels best in your hands, what you intend to hunt, etc.
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Contender
G2
Encore
Striker
Coompetitor