Ages then Seasons. Ages has the much better plot and is more interesting on its own. Seasons benefits from being the second game as the extra bits of the plot really make it more interesting. Seasons has an item that is very useful for the end of the linked game. You also get a boring introduction dungeon turned into an optional bonus dungeon.
Ages is more puzzling, and Seasons tends to have tougher fights. Bosses in Seasons are hard but overcome by brute force (they are the bosses from LoZ). Bosses in Ages give you pause to think about how to defeat them.
I prefer Ages first, although I am biased towards it. Seasons might be good first if the puzzles/confusion as to what to do next in Ages might make you give up.
Sansa backed away from him. "You're awful". "I'm honest. Its the world thats awful."