I would suggest the UR816c, mainly because it is a lot newer and cheaper too. The big drawback (and the reason I run a UR824) is that the 816 only has 8 ADAT channels in, whereas the 824 has up to 16 adat out.
They both have 8 ch out (the 10 ch referred to in the table is bs, just a pair of doubled main outs), and 8 line/mic in.
I’d better recommend a Presonus.
The Steinbergs are good too, but the drivers are much better on Presonus, plus you get Studio One Artist which is better fitted than Cubase AI, and a multitude of plugins. If you do so, make sure you do not install drivers after version 3.6.0, and in both case, think to configure Windows the right way.
By reading the specs, it looks like the UR816C has much worse output converters. Much less dynamic range, worse harmonic distortion. The output quality of the UR824 is really stunning, and one of the few things that can make a digital piano sound as massive as it should.
Oh, let’s hope they will come out with an UR824 mk2 – the same specs, with modern software.