I have tried both long-term. I like the Imperial better due to pressure issues. The regular B17 is stronger due to no slit in it, so I think the regular is better... unless you need the Imperial like I do, which would make the Imperial the better choice.

Break-in would be about the same for either one, and can be accelerated by using a liberal amount of Brooks Proofhide or a similar product.

I found that the B17 in either flavor was comfortable from the start. My opinion is that if it's not working pretty well for you from the git-go, it won't work long-term even with beak-in.