That depends on the programs that are being offered.
This website shows a couple of programs for a small group tour, but you can use it as a guideline to compare with what the joint group tours offered by those operators that you mentioned.
Just want to let you know that since the Cai Be bridge was built, the floating market there is no longer what it used to be.
You can wait until you get into Saigon.
Go down to the Bui Vien backpacker area and check out a few tour operators there before you decide on one.
My Tho - Ben Tre is more of a value, IMO.
But it's all up to you.
I also vote for Ben Tre day trip. Try to get deeper, nearer to Ben Tre city where the cruises are operated on the smaller river instead of the larger freight channel between My Tho and Ben Tre, which is very touristy.
Nhung from Mango Cruises