I would say that the first one is better, but you can also do something like google analytics and use the second one.
Pop-up windows are not a good idea since everyone complains about it all the time online and this is linked with the "Pop-up ads" negative affects in an average user mind.
I would say : Test it. You can try to do some User Research to know if users prefer the first one or the second one. You can do it either by using tools like "hotjar" to look at the user during his interaction and combine it with Google Analytics and Google Tag Manager tool
You could do some classic User Research through observation and UX curves to see what's best.
Also, think about the evolution of your system : Is it better to have a "scroll down" thing (because adding a TONS of info will be not good for your UI maybe?) or a "window from right" (letting you add some new infos that can be useful in a near future).
Also, just thinking about it now as an idea to refine, you could go for a "multiple window" view like in browser : A user can open multiple "tabs" and switch the view to them to see everything he needs (that can be used for comparaison for example).