The drive-line that transmits power from the engine to the propeller influences the reliability and ease of repair. As with outboards, small stressed parts running under water must be more likely to fail than low stressed items running within the boat. If a boat has to be removed from the water for a repair it must be more costly than if the boat can stay afloat.
I am happy with 1/2 inch of steel between myself and the deep blue. I find 5/16 inch of GRP acceptable, there is no way I will trust my life to less than 1/2" of rubber diaphragm - perhaps I am over cautious - you decide.
Engines at the extreme aft end of the boat tend to be the least intrusive into the accommodation, but the further back you place conventional drives the steeper the shaft angle has to be. The steeper the angle the more power is wasted trying to "push up" the back of the boat, and the more likely one is to cause oil leak/contamination problems.
Note the angle of installation. Everything is inside the boat apart from the prop, outer bearing, and stern tube.
Most problems can be dealt with afloat and inside the hull.
Both the remote V drive and the integral type allow the engine to be mounted close to the back of the boat, they also allow the engine and transmission to be virtually horizontal so lubrication problems are eased.
There are potential problems with access to things like pumps, heat exchangers, hoses, and alternators mounted at the "front" of the engine.
Often the stern gear is under the engine so access is difficult and it is likely to be covered in oil. A water leak here involves problems in disposing of quantities of oily water.
The V box is an extra component so it costs more, but there are no real weight or size constraints so it should be reliable.
A "drop in" engine and transmission package popular in small Yachts. Allows an inboard engine where normally only an outboard could be used.
A large rubber diaphragm is all that keeps the sea out, the leg and bevel drive is submerged at all times, the boat has to come out if there is a problem which requires leg removal. Potential lubrication problems in the leg.
Small, highly stressed, parts in leg.
Again much of the outboard mechanism is under the water. Small, stressed parts in leg. Complicated mechanism for tilting up (for prop clearance) and twisting for steering leads, to slack and wear.
Inability to steer without power on leads to collateral damage.
The leg, especially if a rudder is fitted, is vulnerable to damage and hitting things with the leg often leads to transom damage.
Boat must come out of the water to do much more than change the oil in the leg (even then some have to come out for that, especially if the mechanism is bent and will not tilt).
Allows the engine to go anywhere. No prop shaft vibrations carried onto the engine mounts and no engine vibrations/movement to "bang" the shaft about and send noise & vibrations through the hull. Easy to build in a "reduction" gearing.
Wear causes a slow loss of efficiency/performance. Some power loss as heat in the oil. Filtration is vital. Parts can be very expensive.