I haven't had any problems with the junk filter, but that's mostly because I use it for my gmail account, which has an excellent spam filter.
I used The Bat! for 2 years. Really nice client, it had many advantages which no one client had (like grouping the mails by message id - in that time, Outlook and Thunderbird had only grouping by subject or sender. Not by references). But now, Thunderbird offers almost the same features, so absolutelly Thunderbird
That feature is amazing, I almost don't have to deal with spam now on all the 20 email addresses in my account. You can definitely go for it.
Thunderbird is much easier to deal with rules, identities and it's much better with its portable version (I have it installed on my Flash Disk).
Alrighty...i just switched back to thunderbird after a long time with outlook... so...anyone recommend any good extensions? (and yes, after just using it for 1 day again now...i remember that it is much better than outlook IMHO)
I do not like how Thunderbird handles multiple accounts. Plus, it lacks the mail sorting into certain folders like outllook has. For me I have to go with OutLook. I like the built in calendar of outlook. I use it all the time. I tried out Thunderbird but I started getting lots of spam messages and OutLook updates the spam filters every once in a while for MS and also you can create your own spam rules with OutLook to.