My personal preference is Onkyo, but I think there are probably 4-5 brands you go with that are quality, and then it's simply about which functions and specs look most desirous for your setup.
Just a little comparison chart for AV receivers at around the $500 pricepoint. By now, these should be reduced, so you can either save some $$$, or jump up to a the next level or 2 in their model line, or get the newest model year.
http://www.audioholics.com/how-to-sh...-receiver-2013
By the way, I think your budget of $600, is a smart level of investment. You'll get some added features and integration, without overspending for some top of the line stuff that's probably going to be negligible
in your satisfaction with the avr.
Unless you're committed to really shelling out many many thousands for some insanely pricey speakers and the rest of the components- which most people are not audiophiles and the the cost to value is really either to stroke your ego and namesake and just a waste unless you're One that doesn't give a 2nd thought to discretionary spending.
Not to mention, if you wanna build up your system, invest it in a quality speaker. Even if it's done in phases by channel in order of importance
(C, FR, FL, MR, ML, RR, RL, S1, S2, RW, LW, LD, LD2, RC, RD, RD2, LH, RH ) - depending on your setup and processing / # of channels.
You can add to that over time and the item most likely that is going to need updating to handle new technology and types of of connections will be your avr.