I did a trip last Thanksgiving with DD and we really wanted connecting rooms.
Before I did anything I looked at Andre's website and counted how many connecting rooms in each category there was and booked the one with the most, in hopes of getting one.
I made connecting rooms our only request. Didn't care building, floor, anything but for connecting.
I use the TP fax service, included both confirmation numbers and listed connecting rooms as our only request. We got connecting rooms.
So if garden has the most connecting rooms, go with it. If Preferred does, go with it. And ask for it as the only request.
If it's just adjoining you want, I'd go with the one that has the most rooms period. The more rooms in the category, the better odds of getting it, at least in my brain.
I wouldn't count on a switch after arrival to a different category of room.