Its fast, I handle lots of mail and the filters always work, the spam
filters are better than any other client I have had. I tried to use
online webmail but, here is the thing about that (for me): when I need
something I have to be online. Now, my pc is online 24/7 but sure
enough, several times I have needed something and I couldnt get my mail
from gmail one time because either a connection problem or gmail was
down (which is totally rare anyway).

I think it depends on how you use it. With the amount of mail I handle I
couldnt do web mail but someone with less could.