I stayed at both the Canopy and the Hilton during same trip at the beginning and end of a Ring Road trip, respectively. We did 1 night stay at Canopy on Sunday night, so we just parked for free right front of the hotel and were on the road by 9 am, so we never had to worry about it. Overall, Reykjavik is a "newer" city more accommodating to automobiles, and parking isn't a nightmare as with other European capital cities.
We stayed in Hilton for 2 nights (Sunday and Monday), and while not as stylish or convenient as Canopy (aside from the free parking), the rooms are bigger and (at least when I stayed), half the price of Canopy. The Hilton seems to be a popular hotel with [North American] tour groups, and when I was there, it seems tour operators have visitors arrive and stay at the Hilton Sunday night and head out of town Monday morning; or end their tours at the Hilton Saturday night and visitors check out Sunday for their return flights. So Sunday afternoon check-in and Monday breakfast was packed and chaotic.