"The Last Wish" is a collection of short-stories. "Blood of Evles" is the first part of a five-part saga, and the upcoming "Times of Content" is the second installment of that saga.
In my humble opinion, you'd do best if you start with "The Last Wish". It's easier to read, and you'll be able to judge if the literary style of Mr Sapkowski and the translator are something you'll enjoy, without investing yourself emotionaly with a long series that might take years to be translated. Also, if you decide it's your cup of tea, reading the stories adds a lot of background to the saga, and some events (nothing too crucial) are referenced.
I haven't seen the English translations, but personally I enjoyed the short stories more than I did the saga. But those are my subjective views.
Good call, was considering buying one of the books to see if I'd get into it, seeing this topic made me go buy The last wish.
Most of the books I read are from British or sometimes American authors so not totally sure how it will come across in English but it's worth a try for sure, I love the story, lore and background of the characters in The Witcher games, here's hoping the books give as much enjoyment.