Outboard boat motors tend to be more popular for a good reason. They are cheaper to buy and maintain, plus they are generally a more reliable option. That being said, a well maintained inboard can last forever.
The problem is most inboards, especially second hand ones are poorly maintained due to the servicing cost.
Sterndrive legs can be troublesome and expensive if you don't maintain them, the problems become multiplied if you leave the boat in the water for extended periods of time.
The biggest problem is the leg seals deteriate causing loss of gearbox oil and ingress of water. Expect to pay thousand of dollars to fix leg seal problems.
But as I said, maintain it well and you will have no probs. Just get it thoroughly checked before purchase.
Something else to consider is that the engine hatch for an inboard restricts your deck space but on the positive side allows for easier stern access and an option to a swim platform which is a must for fisho’s.
Another big issue with them for me is the danger of fuel (Petrol) vapours sitting in the bilge.
The cost of servicing an inboard like a Mercruiser is roughly around 1.5 to 2 times the cost of an out board.
In general inboard fuel consumption isn't as good as a 4 stroke outboard, but new injected motors are a lot better than the older carburettor engines.
Diesel sterndrives run more efficiently with an ideal trolling speed (7-8 kn) using as little 4-6 litres per hour. Expect to pay more again for noise suppression. You will go deaf without it.
An outboard is easily replaced and you can always sell it if you decide to upgrade to a better,newer or more efficient model. Outboards reliability in recent years have surpassed all previous expectations.
An inboard is going to put the center of gravity nearer the middle of the boat which will help all round performance and give a smoother ride in rough waters, but it will take up valuable space in the boat.
In summing up which is better inboard or outboards depends on your personal situation. If you own a 36ft plus flybridge cruiser you would be best suited with a diesel inboard engine on the other hand for boats between 24ft – 36ft could find benefits for either. If your boat is going to be wet berthed then twin outboards will save you ongoing maintenance costs while an inboard is ideal for cruising but a regular maintenance schedule will have to be implemented.