The White Manta probably is the nicer boat because it is not quite yet a year old. Although the dive deck needs a paint job already, the cabins still look brand new. All the safety and navigation equipment is also state of the art. There are several cabins which are four ppl to a room and some that are two to a room. There is plenty of space in the cabin for storage of person gear although your dive bag gets put away under the benches elsewhere on the boat for the duration of the trip. If the full compliment of 22 divers and 5 DM's are onboard, they definitely need to gear up in two stages. I have been onboard with 16 divers and 3 DM's before and we could all gear up together. I like their DM's who all seem to be friendly and try to talk with everyone. About half are ang moh and half are Singaporean - which usually seems to match the mix on the boat. I am very appreciative of the fact that the more experienced divers are always given the option to dive on their own (i.e., with buddies but not following a DM).
It has been about 16 months since I have been diving from the Samudera Quest so my memory of that boat is not as good. More often, I stayed in their resort so I'll let others comment on that boat. I do believe they have very friendly and helpful DM's although I had some trouble getting permission to not follow them on dives. That's not an issue for many people though.