I have stedmans' and I like it. Good entries, only con is that it spilts the alphabet in two, so you open either A-L or M-Z. It loads faster that way, but it is annoying to look up a C then an O then a D!
I got it for free becuase I got it as a birthday gift. I don't know of other discounts.
I also have "Eponyms" a free dictionary I got off some website. Maybe mytreo.net, I'm not sure. It is a dictionary solely for eponyms (things names after grumpy old men and unfortunate patients) which can be really helpful and make you look really smart!