Originally posted by Norfleet:
Well, in that case, first, I'd suggest taking a nation that is fairly conventional, so you'll get a decent level of exposure to how the game works, and is also fairly difficult to attack. Try Atlantis, or R'lyeh. That will impede the AI's ability to rush you, and you'll be able to experience a full game without being swarmed. Once you get that down, try and go faster. Then move onto land.
For single player, I've found the ocean provinces are great even for land based nations (demo nations, default indie strength). Either of the aquatic mercenaries (Fishermen / Shipwreckers(?)) are capable of taking lightly defended territories; reinforced by the common local tritons, they take more heavily defended ones. Better yet, the leader of the Shipwreckers is a priest - thus letting you build water-based temples next to enemy dominion / territory.
Even without the mercenaries, a decent amount of Water magic seems to allow several of the nations (Jotuns, Abyssians, Machaka especially) to go underwater with enough strength to, again, take a lightly defended water province and then build local aquatic reinforcements - tritons are cheap (resource-wise) and fly in the water. Disposable water cavalry.
Of course, this changes if your SP game includes Atlantis or R'lyeh as opponents.
If Atlantis / R'lyeh aren't in game, though, the water areas have great benefits. Secure temples (if nothing else, a priest with appropriate magic item building them), secure gold incomes, frequent source of nature gems even without searching (Kelp Fortress), and with a rainbow pretender, lots of magic gem sources that probably won't be taken by the enemy.
Again - predicated on Single Player games.