Wells is a good choice and is probably the best two-way English-Esperanto dictionary I've held in my hands. The English in this book is more British than American.
Benson's Complete Esperanto-English dictionary has more detail in it, but it's only one-way, so you'll want either a two-way dictionary or an Esperanto-Esperanto dictionary to go with it.
I also have Krause's Großes Wörterbuch Esperanto-Deutsch which is also one-way, but it goes in the other direction.
I think you'd be happy with any of these (well, assuming you speak British, American, and German) but I've been told that Amazon tends to be kind of expensive for these kinds of things. You might want to look into various Esperanto book services.