Taj Vivanta is in a ridiculous location. Nowhere close to the beach and at a very busy crossroad in town. Looks more like an office building than a hotel, though I've heard they have a nice restaurant.

I haven't stayed at the PH, but my parents live close to the Marriott and its a pretty decent hotel - I use the gym and spa there a fair bit and they have an excellent bakery.

Oh, and in July you're more likely to get whole days of rain than the heat. Don't expect much from the beaches - the sands will be wet and the sea too rough to do anything. I go there a few times a year and always avoid Goa between June-September.