If given choice which would be better Nuremberg Rally Grounds or Roth and Industrial Museum?
I guess it entirely depends on what interests YOU. The Rally Grounds are an important part of world political history, Roth industrial history. I think I would prefer the Rally Grounds, but that is just me.
I have not visited Roth, so can't comment.
Be aware, though, that other than the shell of the unfinished Congress Hall, parts of which now house the Documentation Center and concert hall for the local symphony orchestra, the "Rally Grounds" are not preserved as any kind of monument. There are a few sign boards that provide a historical overview of the premises, but the majority of the land is now used as a public park and fair grounds. You can see traces of the ruins, and part of the grandstand remains (the post-war US army base used it for their high school football stadium), but there's otherwise only sparse traces of it's pre-WW II use. I particularly like the large beer garden located next to the lake, though. A large beer goes down well after visiting the Documentation Center.
I'm not saying it isn't worth visiting. It is...especially if your visit coincides with the annual Nuremberger Volksfest. Just don't expect much of an effort at historical preservation, along the lines of a Civil War battlefield.
I have never been to the Roth Industrial Museum. Maybe it is a gem? I should check it out. Thankz for bringing it to my attention. My brother from the USA liked the Nürnberg Rally Grounds and the Dokumentationszentrum Reichsparteitagsgelände. He also wanted to go to the Eagles Nest and we did. He is a bit of a WWII history buff. Honestly for me time is better spent exploring the Nürnberg old city, the Kaiserburg Nürnberg, Biergarten, cafes, Rostbratwürste and shopping (did this with my brother too in one day), and for the Eagles Nest the Nationalpark Berchtesgaden and Königssee. Unless you have a real interest to visit the old Nazi sites and it is a must for you, there is so much else to see and do, but you can probably fit these sites into your itinerary. Maybe the Nürnberg Toy Museum for European toy history?
I agree that the Rally Grounds themselves aren't much to see (although I certainly got a shiver doing so), but the Dokuzentrum was very worthwhile and I spent several hours there.
There is actually quite a bit to see around the Rally Grounds, and it is a pleasant walk. There is some interpretive signage around the Zeppelin Field, the Tribune and Duzendteich, but it helps to know what to look for. For a better understanding of the chilling significance of these sites and others in and around Nuremberg, read Showcasing The Third Reich: The Nuremberg Rallies by Andrew Rawson, available via Amazon and iBooks.
If you were not aware of this website: http://www.thirdreichruins.com/nuernberg.htm
By the way, here's my favorite example of a NS-era structure refurbished for modern use. You can clearly see it if you drive into Nürnberg on B4 from the southeast.