Assumes:
(1) Serious Cruising/traveling mode
(2) Plan to rely on the motor
Exceptions:
(A) people that plan to "pure sail" (e.g
http://www.oarclub.org/ ) or are voyaging and only looking to the motor to get them through calms or aganst a current into a port thay can't sail into.
(B) few designs that provide a sealed motor well that the outboard fits into so that it is in essence a 'sail-drive' that is easily removable and serviceable. It can also be removed a plug inserted to fair the hull and reduce drag. This is actually a reasonably easy modification on many hulls that are good sailors but only have transom mounted outboards as an engine option.
(C) Few designs have inboard motor wells and if you have a xtra-long shaft(25") they can be used if VERY rough conditions and will preform pretty much like an inboard. They can be a pain to get motor in and out and to rig controls but they are a nice compromise.
(D) Daysailing/Inshore sailing
Transom Outboard+:
(1) easy to service
Transom Outboard-:
(1) when you REALLY REALLY need it the prop is coming out of the water and you are leaning over the tramsom playing with controls and not able to focus on other boat chores or keep watch ahead.
(2) The weight is placed in a terrible place at the extreame end of the hull.
Inboards+:
(1) see outboard'-'
(2) Diesel is an option, unlike outboards
(3) weight is in a good location
Inboard-:
(1) can be very difficult to work on in many designs that 'shoe-horn them deep in the bowls of the boat.