@profoundlynerdy I use a combination of them. I have a computer at home that is online and is on 24/7, it has fetchmail running that retrieves mail from for all my accounts. Most of the time I just ssh there and use mutt.
However on my laptops I'd like to have some offline access so I use Thunderbird that retrieves emails and stores them locally.
I don't like Thunderbird for being resource-hungry so I'd like to get rid of that, I should probably sync the mail dir from that computer and use mutt.