BKK Airport to Koh Chang

Our bumpy flight from Vientiane to Bangkok arrived at night so we decided to spend a night at an airport hotel before boarding the bus to Koh Chang the next day. It's a 5-hour drive from Suvarnabhumi Airport to the ferry port, followed by a 40-minute ferry ride to Koh Chang then however long it takes to your accommodation.
At Bangkok's Suvarnabhumi Airport, you can find the bus ticket counter to Koh Chang on the first floor by Gate 8. Buses operated by Burapha leaves at 7:30 am, 11 am, and 2 pm. Another operator charges 600 baht for one way and 900 baht for round trip departing at 7:50 am, 11 am, and 2 pm.
Bangkok airport to Ko Chang bus schedule Suvarnabhumi Airport to Koh Chang bus schedule
We got the 11 am van for 600 baht each, all inclusive from airport to hotel drop off on Koh Chang. We waited by the bus ticket counter to Koh Chang on the first floor by Gate 8 and were called to board the 10-person van parked outside. The 5-hour drive to the ferry pier was not very scenic - the road was pretty straight and flat so the driver was going 100 km/hour most of the time. There were two 20-minute snack/bathroom breaks in between.
At 4 pm, the van drove onto the ferry and we could get off for the 40-minute ferry ride. When the ferry got to Koh chang, we got back on the minivan and were driven to a travel agency where a lady collected our bus tickets and asked about our hotels so the driver can drop us off. The roads on Koh Chang are narrow, steep, and windy between the main beaches. We didn't get to our hotel on Lonely Beach until 5:45 pm.
Koh Chang to Central Bangkok

As for the return trip back to Bangkok, there are VIP buses advertised for 290 baht. We booked a door-to-door minibus to our hotel near Sukumvit MRT Station for 750 baht each, departing at 8:30 am. Getting dropped off the airport will cost 650 baht. Like the way to Koh Chang, it took about 6 hours from Koh Chang to Suvarnabhumi Airport and an additional hour to Sukumvit, mostly due to heavy traffic.