I'd do the Gritti at 50% off now, while it is available.
There will probably be a special come June or July that will be less than the 50% off rate. The E&R is $250 and the Danielli is $320 internet rates for Feb.
In August, I would heavily weight the quality of the A/C system in my choices. I recall seeing some complaints about Venice A/C in some of the hotel reviews.