I'll have to agree that you will never have a "perfect" speaker. The question is actually not a very good one as it is too broad to be aswered by a group and arrive at any kind of a concensus. It would be best to limit it to your acceptable price level ($600 in your case). The best speakers that I have heard around $600 must be the JM Lab Chorus 707s, which have been favorably compared to most everything less than $1000, making them quite a great value as well.
I change speakers quite a bit and so don't have one that has had a lifespan of more than a few years regardless of their quality. The last were Tannoy D700's and the newest will be JM Lab Electra Be speakers, either the 927Be or 928Be.