What's good: Selecting a boat based on it's deck area not just on length. Don't ignore the beam and layout of the boat since deck area is paramount for diving. A good strong bottle rack is great to have. An A frame can free up space on the deck as you can store dry boxes and life rings. Consider recovery options, one with a ladder is good but try to consider the height of the tubes above the water line if no ladder available. Some tubes are very high when viewed from the surface! Colour - red is crap in sunlight!!!! Grey is good. Engine - I am swapping away from 2 stroke for a 4 stroke for economy reasons.
Just my ha'penny worth.
Don't ask about makes - you will be surrounded by worms.