I may be in the minority, but I like Cabo Diving. I've been diving (annually) there for almost ten years.
Local Diving isn't bad off (small) boats. Neptune's finger is my favorite. Pelican Rock is a close (logistically) second. Sand Falls is a bit underwhelming.
Strongly advise taking the bus trip over to Cabo Pulmo (organized through one of the shops) and diving over there. IT IS SPECTACULAR!!! Saw a whale shark out there one year (although it was later in the year than July).
July is hot and humid in Cabo, but I would bring a 3MM/shorty (or rent). Not saying you couldn't go in less. Up to your personal tolerance.
I dove two July's ago and saw two white tip reef sharks, barracuda and a whole lot more at Neptune's Finger.
Also, an option, there is some shore diving at Chilleno Beach (Reef). It's a little sandy, but there is a nice wall (starting depth around 30 feet). Last time I dove there, I saw a couple of Tuna which was pretty neat. There is a small dive shop on the beach where you can rent tanks and weight. I would bring everything else. Not bad for blowing bubbles.
Hope this helps!!