The cruises compared here
Both boats sail the same central stretch of the Chao Phraya, past Wat Arun and the Grand Palace. That is where the resemblance ends. One is a ferry you step on and off all day, the other is a two-hour sitting with a buffet.
People tend to compare them on price, which is the least useful measure here. Compare them on time of day, on how much freedom you want, and on where you have to be to board.
1Daylight against evening
The tourist boat is a daytime service. The listing gives its hours as 8:30 am to 7:15 pm, with a boat roughly every 30 minutes. You see the temples and the riverbanks in full light, from an outdoor terrace or from covered seats inside.
The dinner cruise belongs to the end of the day. The sailing on sale when we checked left at 5 pm and came back two hours later, and the listing also describes a later evening voyage. If the city lit up at night is what you are after, only the dinner cruise can deliver it, and only on a late enough sailing.
2Getting off against staying put
The day pass gives unlimited rides for one day across 11 stops. The listing mentions the Reclining Buddha, the Tha Maharaj shopping complex, Chinatown and the flower market as places you can reach from them. Used that way, the pass replaces several taxi rides as well as a cruise.
The dinner cruise is a closed loop. You board at Asiatique, stay at your table or on deck for two hours, and get off where you started. Nothing wrong with that, but it is an evening out and not a way of visiting anything.
3Commentary and comfort
Neither boat offers much explanation. The tourist boat has an English audio guide through headphones, plus pier announcements in Thai and English according to the operator. The dinner cruise lists an English-speaking guide and an English audio guide by QR code, competing with live music.
On comfort the listings leave gaps. The tourist boat is described as having both outdoor and indoor seating and is listed as wheelchair accessible. The dinner boat is not described at all and is listed as not accessible.
4Where each one boards
This is the practical trap. The dinner cruise checks in at Asiatique, Warehouse 3. The tourist boat voucher is accepted at every pier on the route except Asiatique.
The operator says its route is extended to Asiatique in the evening, but it does not publish from what time, and the dinner check-in for a 5 pm sailing is at 4:30 pm. Do not plan on riding the tourist boat to your dinner cruise unless you have confirmed the timetable on the day.
5Our pick for each kind of trip
With one day in Bangkok, buy the day pass and spend the money you save on dinner ashore. You will have seen more of the river, in better light, and visited the temples along the way.
With three days or more, the two fit together well: the tourist boat on your temple day, the dinner cruise on another evening. If you travel with someone in a wheelchair, the tourist boat is the only one of the two the catalogue lists as accessible, and you must say so when booking.