Gunpowder,
I'm a long time user of Constant Contact, but have never used Vertical Response.
I found Constant Contact intuitive to use from the beginning. They have a very responsive support department as well. Overall, I like CCt well, with a few exceptions. Perhaps most pertinent to you from your comments, is that it is increasingly sluggish when I access it over a dial-up connection. It is the slowest site that I deal with on a regular basis. I have called their tech about it, and haven't been able to resolve the issue. This is a change over time. It used to be better.
It is possible that the problem has to do with new interactions with my firewall, so you may not find it to be an issue yourself. I don't know that Vertical Response is any different, but I'd suggest you be sure to check that out for both.
Best wishes,
Sasha