Elaugaufein
Member
In the order they were released.
It will be hard going back to the older games after playing the newer ones.
D3Vita is still very playable. Disgaea2's postgame was even grindier than d1s when it came out and the PSP version of d2 did nothing to alleviate it, its probably the most luck dependent grind fest in the series. D1: PSP has glitch that let's you skip a looooot of grinding, D1S and D1 aren't as random as D2 but there's still a lot of things that can screw you over (the item world code is a lot less refined and its possible to get unsolvable levels) and its a looong grind without much in the way of shortcuts.
D4 was actually more grindy than D3(original or Vita) but the portable version is alleviating that significantly.