Oh well.. this has been asked so many times... I think if you browse the forum for old thread, you'll find millions.
I don't know, actually I think maybe it's better if you get them in order of appeareance... Opinions vary and for example I can say 'get Dance of December Souls and Brave Murder Day' because those are my faves, but then another one comes and says 'you should get Discouraged Ones' or etc, and you'll end up getting mad and very confused, hah, so you can do that or try listening to some of the samples on the official site of the band and then maybe you're able to decide which one to choose. It's not the same buying BMD or VE, so perhaps you'd better take a little listen to some of the songs and then decide, I don't know... just a suggestion.