I have used them all - or almost - and I confess the first time I tried Thunderbird I did not like it. However after close inspection of features and after using it, allways comparing with others, I have to admit this is a great email client for one - like myself - that do have several mail accounts on different servers. I only use it on an IMAP configuration and it works like a charm as I can not only keep the messages I want on the servers instead of having them on my machine, delete the ones I do not need and even receive a message on a server and forward it from a different one, transfer messages from one server to another, on the fly, etc. I use the portable edition and have it installed on a USB pen, is fast enough and very reliable. The management of messages is top notch, as is the management of the address book, either in groups or by individuals. As a free program, it must be considered the best of them all. I have used Opera mail client prior to switch to TB and I feel that is the only contender TB do have. I prefer however TB.