Being in manufacturing and MT being my home state, I have and have had a few defiances over the years. When Glen owned it without a question everything about defiance was absolutely excellent. I know when Bob Beck bought it a lot of my friends who dealt with defiance daily trended away from them because of the change up in CS and leadership. Also a few actions slipped through that shouldn't have. I know the few very limited and I mean limited QC hiccups were remedied, but more than anything how Defiance treated their dealers because of the internal change up hurt them. Also jacking action prices up $500-600 overnight didn't go over well. I believe the quality is still there but id have to ask my sources how the current actions have been.(PM me if you want.)
Personally I went away from them because once Glen was gone, I just didn't like how the CS applecart got upset. Plus I found Kelbly Nanooks to be what I really wanted in an action from a feature vs price standpoint. I will never sell my OG AnTi or OG Tenacity and have no complaints really other than I feel at $1500+the bolts should come nitrided. If I ever build another rifle I'll choose Kelbly.
I have heard nothing but positive things about impact and they have a massive following. I think you'd probably be more than happy with an impact. While I don't think you can probably go wrong with either, In todays market I wouldn't choose defiance, because like I said I found another action I like more.