About Jamaica being a great and convenient location ...
That's only half the story. What follows is a long and geeky explanation, but it also happens to be very accurate.
Each village (except for Trinidad North) is made up of 6 numbered buildings, and each numbered building is comprised of four smaller (unnumbered) buildings. So each village is on a pretty spread-out piece of real estate.
It is true that Jamaica 45 is about as close as you can get to Old Port Royale without paying for preferred location (same goes for Aruba 51 and Martinique 22, by the way ... identical down to one one-hundredth of a mile, I've measured it from aerial photos on a runners' website).
So yes, Jamaica 45 is as close as you can get without paying extra. HOWEVER, Jamaica 41 is as FAR as you can get from Old Port Royale, except for the pirate-themed rooms in Trinidad South.
So if you request Jamaica, you COULD get the closest standard room to Old Port Royale ... but you COULD get the farthest standard room from Old Port Royale.
The same goes for Aruba. Aruba 51 is a mirror-image of Jamaica 45 ... it's exactly the same distance to the bridge over the lake as Jamaica 45 is. So Aruba 51 is as close as you can get in a standard room. But Aruba 56 is (just like Jamaica 41) as far as you can get from Old Port Royale in a standard room.
So if you request Aruba, you COULD get the closest room or you COULD get the farthest room.
That brings us to Barbados. Barbados is what I'll call a "middle of the road" location because you can't possibly get the farthest room from OPR, but you also can't possibly get the closest room to OPR. If you're not a gambler, this makes Barbados safe ... you won't "hit the jackpot" with a close room but you can't get stuck with a very very far room.
Half of Martinique (buildings 21, 22 and 23) are standard rooms. Building 22 is in the club with Jamaica 45 and Aruba 51 as the closest standard building to OPR. But since there are only 3 standard buildings in Martinique, if you request Martinique you have only half as much chance of getting your request compared with requesting Aruba or Jamaica or Barbados because those villages have 6 buildings each.
Forget about requesting Trinidad North and the other half of Martinique (buildings 24, 25 and 26) because these rooms are in the "preferred location" booking category ... they cost more per night than a standard room because of their proximity to Old Port Royale. And forget about requesting Trinidad South because those are the more expensive Pirate-themed rooms (again, a separate booking category).
As far as water view, I agree with all of the above opinions that it's not worth the cost due to the exterior corridors and the lack of a private view. Strangely, Disney does not allow you to pay two up-charges to reserve and book a preferred location water view room. If you want a water view room in a preferred location building, your only way to do it is book one and request the other and then hope to get lucky.