The long trail of visits for Show HNs come because they stay on /show a lot longer than it'd stay on the frontpage. So while it can be featured on the frontpage for an hour or two, that same submission could stay 2-3 days on the Show HN frontpage, even as it dropped of from the actual frontpage.

I think the frontpage is both a lot harder to get into, faster to get dropped from there, but obviously also has a lot more traffic. But the traffic from Show HN frontpage seems to engage more (again probably because of the mindset) and it stays there for a lot longer.

Personally, when I want feedback about the idea and implementation, I'd go for Show HN, because you're out after comments and discussions then, not just traffic and views. But if traffic/views are what you care about, regular submission would do "better".