Like Rafael said, download the trial first before shelling out the dough. If you have or plan to have any paid-for web hosting, there's often services included that may have some merchant-related scripts/services. CoffeeCup has a shopping cart program in the works right now that I do believe will be tied to Paypal (very much looking forward to see that one).
I'm sure there's pros and cons to each app, but usually the biggest issue is adjusting from what you're used to. I have FrontPage, Expression Web & CoffeeCup's editors and sometimes hop back and forth, depending on the project/scenario. I'm not trying to turn this into a sales pitch, but I can tell you having "free upgrades for life" definitely isn't in Micro$oft's list of features. I think it may even be the opposite. "Buy now for a lot, and spend even more on the next release."
Everyone has their preference though, so take advantage of the trial download so you don't regret buying anything. Or go all out like I did and order all the apps for a major discount (probably still less than Expression Web alone off the shelf).