Both are equally stellar. 1 plays like a typical spaghetti western while 2 plays like a western drama of sorts, so you’ll find the tone a bit off-putting at first and the story doesn’t carry a lot of the heft that 2 did. Mechanics such as Honor play almost no role in the story so it’s a more linear experience, too.
When it comes to gameplay, you’ll most definitely enjoy 1. I’d say the first game plays a bit better; the controls are more streamlined, and I found myself making a lot of mistakes when it came to 2’s weird interaction menus and such, so it’s a nice change of pace. Aspects such as hunting and side stories are naturally not as fleshed out, but that’s up to personal preference. They’re still pretty good and engaging.
If you ever wanted to pick up RDR1, now’s a great time. We long heard stories of how hellish the development of the game was, so it being available on modern systems is a great achievement. We have yet to see how it would perform on the Switch however.
Aside from poorly documented hardware, one reason why Xbox emulation is in such an early state was simply lack of interest. The Xbox had a meager first-party library and what exclusives there were, were already available to play on every Xbox released ever since via back compat.
I think a more tragic case would be if MGS4 was ever re-released as part of the Master Collection ports. That game was designed from the ground up for PS3, and runs terrible even on the custom RPCS3 builds designed specifically for it.