Automatic trannys and diesel motors.. good for coffee or bad headache?

Hi again..
I am looking at a decent deal on a HJ60 diesel with an automatic tranny.. I have never really liked AT's but thought I could get an experienced opinion..

so..
Is the toyota automatic any good?? breaks alot?? much less fuel economy??
Has anyone here done the switch from auto to 5 speed.. How hard is it?/

Also, while I am at it I also wanted to ask if anyone really knows: which is the best diesel motor that toyota ever made? Is the 6 cylinder as good as the 3b?? I am not crazy about super power.. but I am crazy about durability.. I like small efficient motors that work super hard and go forever..

Thanks again.
Islando