Usually late April through September have good conditions but as the summer progresses there is more opportunity for tropical weather. As to current, I have been on these wrecks with little current and a few times seen the mooring balls nearly dragged under by current. The Gulf Stream just does it's thing, sometimes it sweeps out a little more and other times it hugs inward.
I have for years done an annual trip, actually was just down there a month ago. But not my old time road trip. I usually start in Jupiter or even the panhandle if doing my Heavy Metal tour (Oriskany, Spiegal, Duane, Vandie) and then work my way south to the Keys. These days I use Conch Republic (Tavernier) for my taxi service. For the Vandie I have had success with Captains Corner.
Weather allowing late August is cool because you can get the Grouper Aggregation in Jupiter and WPB and then hit the Keys. Up on the Gold Coast when you hit your dive site the captain will yell DIVE, DIVE, DIVE! But anywhere in Florida it is DRIVE, DRIVE, DRIVE. There are no integrated resorts to speak off and in terms of $$ and dive count, just go to Cozumel. Of course, Cozumel has nothing like the Spiegel but at least the natives are friendly and there is happy hour!
