I can't speak to Little Daddy's or Chuck and Robbies since I haven't dived with either of them, but I have dived with Splash twice over two years for a total of five weeks so I know that operation very well. In fact, I just published a trip report a few weeks ago covering my trip to Placencia last June (see
Long overdue trip report--Placencia in June.)
Both times at Splash there were a fair number of people involved in all stages of the certification process, from brand new first time in the water divers to those finishing up their open water dives via a referral and all points in between. For the first timers, Splash uses owner/operator Ralph and Pattie's pool behind their house before heading out to the cayes to do the dives in relatively shallow water. There are three or four instructors on hand who double as dive guides when they're not instructing. The classes all looked to be pretty small, ranging from one individual student who was learning how to dive while she was working a summer intern job at a banana plant, to a newly married couple on their honeymoon to a family of four. I don't think I ever saw a class bigger than four. I took several advanced classes my first time at Splash and there were never more than two divers in mine and once there was just me and the instructor.
You can go as big or small as you want in Placencia. The high rollers stay at Francis Ford Coppola's Turtle Inn, which is just up the road or Chabil Mar right across the street. At the other extreme, there are what appeared to be youth hostel type accommodations down in the village. Lots of choices in between. Personally, I liked the cabanas at Dianni's Guest House for $40 a night in the low season. The rooms there were even cheaper, but I like a cabana. For another $10 per night, you can get a cabana with a view of the beach right around the corner.
Perhaps the others do it too, but Pattie can help with selecting accomodations and reserving flights to and from Belize City. They'll even pick you up and drop you off at the airport as well as where ever you decide to stay. And as I noted in my trip report, Placencia is a wonderful jumping off point if you're interested in seeing jungle, ruins, and other above water stuff.
Belize is a great place to learn to dive. Warm water, good visibility and calm seas all make for pretty easy diving.