I've been on both the Aggressor boats and the Explorer boats. I've done the T&C Explorer twice. The actual boats and diving are pretty similar. Nice dive decks, good divemasters / captains, rooms are very comparable.
Where they are different is in food. Aggressor is definitely a step up in that respect. Other than that, the Explorer boats are very well run indeed and you wouldn't find the actual dive experience to be much different.
They do have a slightly different crew structure:
- Both have a captain
- Both have a cook
- The Explorer boats have a Purser who generally takes care of the store and is perhaps less of a divemaster; I think they might be sort of in charge of the housekeeping efforts. They have two dedicated divemasters who switch out each dive to watch the group.
- Aggressor doesn't have a purser, they have instead three divemasters who swap out each dive. Aggressors usually have a Photo Pro on board and both boats usually have a videographer.
- Explorer boats usually have 6 crew members, Aggressor usually has 5; the Explorer has a dedicated Engineer on each vessel. On Aggressor, the Captain will usually do double-duty as the Engineer.
- Many of the Aggressors will have more than one crew member who actually has a captain rating.
As I said, mostly similar and Explorer is usually $400-500 cheaper. If the food is really important to you, definitely go Aggressor. Otherwise, I personally would flip a coin, they are both top-notch operations. My last trip in March on the T&C Explorer was fantastic - Captain Jean Francois and crew were awesome. I always look at both Aggressor and Explorer for my trips, but I have to admit, if one is cheaper, that's the one I'll do.
Have fun,
JP