Take away the Robinson hate and the comparison becomes much more interesting.
The avionics are almost a wash if you spec the 1060 TXi in the 66, although you can't beat the integrated engine instrumentation and FADEC in the 505 (rumor is that Robinson is working on some new engine instrumentation).
Most significant, if you option out the 505 so that it matches the box stock 66 (leather, carpet, door openers, headliner), plus AC for both (but spec. the available lightweight Lithium battery for the 66), you wind up being able to haul 911 lbs of pax/baggage 350NM in the 66, while the 505 limps along with only 774 lbs for a paltry 306 NM.
Plus the 66 is a more mature product in that you can get an autopilot and aux. fuel systems straight from the factory today (fly even farther more easily).
However you slice it you'll pay less out the door for a 66.
But the 505 will hover higher/hotter, go faster, and be more comfortable with that flat floor and only 3 on board
