In my two trips to Koh Lanta, I've dove with Andaman Dive Adventure. In my most recent trip, mid-April to early-May, I dove with some of the other dive ops, Lanta Diver and Koh Lanta Diving Center, because there weren't enough customers and the dive ops start to pool resources toward low season, which starts in May. I still dove through Andaman, and with their guides, but we were on the other dive ops boats.
Lanta Diver is the biggest operation. I think they have three boats, one of which is a high speed yacht, specially built for diving. It's pretty luxurious, with chef on board (for omletes!), and cuts the trip out to Hin Daeng and Hin Muang down to only 45 mins... if there aren't issues with the engines overheating, then it's about the same as the normal boats, 1.5 hrs. For photographers, there's really isn't a place to set up the camera and leave them unattended. The dining tables work for setup, but leaving them on there presents a risk. My camera, in housing, was accidentally knocked to the deck. Thankfully, no issues and I'm just using a G12 with housing, so it's not pricey equipment. There are dedicated wet "buckets" for the cameras, but they're out in the sun and the water gets warm/hot. The normal boats have more space for setting up and cameras go into a dedicated bucket, though once all the dives are over, the buckets are also used for cleaning equipment, like masks and dive computers.
Koh Lanta Diving Center's boat is a normal boat. There aren't good places to set up camera equipment.
Andaman Dive Adventure doesn't have a dedicated camera area, but the dining area serves this purpose well. There's a dedicated bucket for cameras.
Of the three, I like Andaman the best for camera set up and crew camera handling.
For dive sites, Koh Ha and Hin Bidas are the two within 1+ hrs. Hin Daeng and Hin Muang are 1.5+ hrs out. Hin Klai, if you're lucky with current, is sometimes visited as a second dive on the way back. (There are tons of "Nemo" clown fish there and the occasional Zebra/Leopard Shark.) Phi Phi Viking Bay sites were murky the two dives I did there - vis was 3-4m. My favorites are Koh Ha #5, Hin Bida Nok and Hin Klai. Hin Daeng and Hin Muang are renowned for mantas, but I found diving there boring if no mantas show, as it's constantly moving around the pinnacles in search of them... not much opportunity to shoot macro.
All dive ops provide pickup. The further you are away from the dock, the early the pickup is. The dock is by Go Dive Lanta on maps. I stayed nearby Andaman Dive Adventure, so I just showed up at the shop by 7:20 AM, 6:20 AM if heading out to Hin Daeng and Hin Muang. The boat leaves around 8 AM, or 7 AM for Hin Daeng and Hin Muang. After the boat briefing, there's breakfast. After breakfast, it's a nice ride out to the dive sites. I usually chat with other divers for a bit, then prep my gear. I prep my camera about 30 min before arriving to the site. 15 min to the site is usually when the dive site briefings are held. Splash time is about 9:30 AM. Dives range between 50 min to an hour. Surface interval is about an hour, when fresh fruit is served. After the second dive, lunch is served on the way back.
I, personally, like the slow pace to and from the dive sites, as there's no rush to set up equipment or clean up equipment.
I brought my own gear and it was nice to store my gear at Andaman's shop during my diving with them. A couple of days before leaving, I washed and dried my gear overnight. There was plenty of space.