The Shin Megami Tensei series may be numerical but it doesn't really tie together, so you don't really need to worry about missing out of story elements. Each game is seperate except for obvious examples, like SMTIV and SMTIV:A. Personally, I'd say IV, IV:A and Strage Journey Redux just to get a feel for the series and Devil Survivor Overclocked and DeSu 2 Record Breaker for good spin off games. All of them are on the 3DS but good luck getting them physically as, ever since SMTV and the remake of SMTIII were announced, the physical prices have sky rocketed. They remain the same price as ever on the Nintendo E-Shop.