In case of Guilty Gear I don't see a clear option, at least with my knowledge of the franchise. Maybe Sol's stage from the first GG, this one, which would be funny because of the statue of liberty, lol. Looks cool in my opinion.
Paris AC from GG XX would be a nice option for me:
From Guilty Gear Xrd I particularly love Heaven's Edge
The stages from the new Guilty Gear are looking great in my opinion, specially the first one that appears in this video.
For Devil May Cry, I think that there's no doubts. The top of Temen-Ni-Gru from DMC3, arguably the most iconic place from the franchise. I didn't find a better pic, sorry.
In fact I think a DMC stage could be based on the entire tower, or some parts of it. It could be like DQXI's stage, which is like a tour. Temen-Ni-Gru could start at the bottom of the level and then visit some places of the tower, the final part of the stage would be the top, of course. It would be cool, almost all of DMC3 takes places at the tower.