Well the DS/3DS Harvest Moon games are easie to find in stores than trying to track down an old Playstation Harvest Moon game.
Just anwer the question.
What is a good decent Harvest Moon game for the DS/3DS to get into to get used to the gameplay?
I don't understand why you want a recommendation besides New Beginning. No reason not to get the latest (and widely considered, one of the greatest). If you want to save some bucks because you just want to try HM out briefly... emulation.
A New Beginning is by far the best farming-focused Harvest Moon since A Wonderful Life on Gamecube. The Rune Factory games are the way to go if you want more RPG elements, but there's no reason to look at anything other than A New Beginning for farm games.