I'm currently looking to upgrade to a new e-cig as my trusty 401 doesn't quite cut it anymore. The batteries are a right royal pain!!! Now I've got 2 in mind, either a 501 tank or (you will have to excuse me if I get this wrong) an ego tank (both liberty flights website) With still being new to this I am still unsure what to look for or which one is the better of the two. Thanks in advance