IMHO if you do just range shooting, the AR is by far the best and most versatile platform of those listed. If you need to be off-range, the AR isn;t even a choice though.
Of the other rifles listed, the SL8 would be my choice. Even with FN Sports/R.Nichols being the importer, you'd be better off than trying to deal with RobArm who are notorious for being downright hostile to their clients post-sale and there have been a good number of "help - problem with my XCR" threads here over the last few months. The SL8 is an older product and more of a known quantity IMHO. Though the XCR is a cooler looking rifle.
Just my $.02 worth.